Before you make up your mind and decide to become an Assassin consider the advantages and disadvantages of being one.

Advantages:
Poisoning gives you an edge in combat both versus monsters and people.
A high level Assassin with a supply of deadly poison can make a good living in town poisoning weapons for a fee.
A surprisingly high number of people have NO CLUE about the power of poison, so you'll be able to 'enlighten' them in combat.
You will have lots of friends on the dark side (both PKs and Thieves LOVE poison).
Generally you will have no problem finding a guild to join (your art IS appreciated).

Disadvantages:
Poisoning is bad for karma. Many people will avoid you thinking you're a thief, hence the loss of many potential customers.
Poisons CAN be countered, so you can't rely on poison alone against an experienced person.
You will not be very efficient at your trade until you reach low 80s in Poisoning.

Character Creation:
So, you've read everything and still want to become one? Alright.

You start a brand new wannabe Assassin with 45 Strength, 10 Dexterity and 10 Intelligence. Now it's time to shape your future path. The key to becoming a successful Assassin is getting your own poison potions, that means that starting with 50 Alchemy is a must. The second skill may vary, if you want to be a magic user then go ahead and invest the other 50 points in Magery, if you want some extra cash, then pick a money-making skill. I would personally recommend Magery.

"How can I become an Assassin without having the Poisoning skill?"

"Poison is an Assassin Best kept secret?"

"How can I become an Assassin without having the Poisoning skill?" -- Well, Poisoning is easy to train early on, so you don't need to invest any of your starting skill points into it.

As far as the city, I would recommend Moonglow.

For a starting point There he is, newbie Alchemist/Mage/Wannabe Assassin standing in Town with no clue to what to do.

Fear not, the help is on its way.

First of all, get used to the fact that both Alchemy and Poisoning take time and money. If you have a guild or an established character to rely on, great, if not then I would recommend escorting NPCs (via the Moongates) as your main source of income.

Start practicing Hiding early on, and never stop doing that. A good Assassin should be able to hide anywhere at any time.

As you Train the skills of Alchemy and Poisoning Remember that the gains and skill to switch to next level of poison is as such

0 to 30 = Lesser poison
30.1 - 68 = Regular Poison
68.1 - 94.0 = Greater poison
94.1 - 100.0 = Deadly poison

Your first task is to get some initial training in Poisoning, and the NPC Thief Guild master ( Haven Thief Guilds master is down main street to the T in road go right to next corner he is in building straight ahead of you ) is ideal for that. For mere 300 gold he will train you to about 30 Poisoning (money well spent).

From this point you will need to stock up on Nightshade (usually not a problem), grind the poison potions and use your skill.

What to grind: although Lesser Poison ( 0.0 skill to 31.0 skill =Lesser poison ) is more costly, I would recommend grinding Lesser Poisons, because at this point in training it will advance your Alchemy skill. As you grind and gain in alchemy you will produce potions that you can use to advance your poisoning skill. Remember to make healing and curing potions too for extra gold and for you to heal and cure from mistakes in the training where you poison your self.

What to grind: although Regular Poison ( 31.0 skill to 68.0 skill = Regular poison ) is more costly, I would recommend grinding Regular Poisons, because at this point in training it will advance your Alchemy skill. As you grind and gain in alchemy you will produce potions that you can use to advance your poisoning skill. Remember to make healing and curing potions too for extra gold and for you to heal and cure from mistakes in the training where you poison your self.

What to grind: although Greater Poison ( 68.1 skill to 94.0 skill = Greater poison ) is yet more costly, I would recommend grinding Greater Poison ,because at this point in training it will advance your Alchemy skill. As you grind and gain in alchemy you will produce potions that you can use to advance your poisoning skill. Remember to make healing and curing potions too for extra gold and for you to heal and cure from mistakes in the training where you poison your self.

What to grind: although Greater Poison ( 94.1 skill to 100.0 skill = Deadly poison ) is the most costly, I would recommend grinding Deadly Poison , because at this point in training it will advance your Alchemy skill. As you grind and gain in alchemy you will produce potions that you can use to advance your poisoning skill. Remember to make healing and curing potions too for extra gold and for you to heal and cure from mistakes in the training where you poison your self.

These Assassins seem somewhat arrogant and indestructible

Ever thought, "These Assassins seem somewhat arrogant and indestructible, I can kill any man, woman or beast alive, I'm bound to be an excellent assassin."? Well, fortunately, the assassin is a far more flexible character than you could ever imagine. Too many skills increase the danger of the lower skill level range failing at a crucial moment and can unravel your effort so far.

You must be a Grandmaster in tactics and a chosen blade skill, because nothing beats hiding in the shadows with a blade covered in poison for a serious life-threatening diversion. Those are your three basic skills: hiding, a weapon skill and tactics. Fencing or Swordsmanship skills are supreme in administering poison, the kryss, dagger or katana are the fastest weapons in the game. Additionally, Anatomy has several beneficial offerings and is a great help with its damage bonus increasing the rate at which you can dispatch your target. Fast kills are a must because a dead body is safer than one still moving and fighting You can either finish the job with these skills, or swap to another style like wrestling, archery, mace fighting -- Regardless, the fact remains you can prevent an attack for several seconds by administering poison at any time, poison being the real killer one way or another.

Also you need to decide on your weapon skill. I would recommend Fencing (very Assassin-like (Dagger)). Havens countryside is perfect for the newbie to train his fighting skills. While in haven you can walk around picking up reagents and fighting mongbats, lizard men, zombies and horde minions .After your like 60 skill move to Moonglow. Moonglow countryside is perfect for the newbie to train his fighting skills Start with the hinds in the Hind Valley, then move on to the Timber wolves in the Wolf Valley. Once you get a little better, pay regular visits to the graveyard, sometimes it will spawn Skeletons and Zombies (and rarely Wraiths and Liches) for the added excitement and karma gain.

Moving on:
After a while you will be an Expert Assassin, Journeyman Alchemist, Journeyman Rogue (hiding), Expert Fencer, Journeyman Warrior, and (hopefully) Journeyman Mage.

Now when you can poison weapons with good success, is the time you start hunting. As your hunting grounds I would recommend the forests east of Britain and north of Yew. Make a few Regular Heal potions and Regular Poisons, stock up on reagents, recall runes, and get that suit of Bone Armor. You are ready. First I will recommend to look for Orcs (not Mages or Lords), Ratmen, Lizard men and Ogres (if you like adrenaline rush).

Use your weapon to inflict the poison (even Regular Poison will help), use the Regular Heal potions to keep you alive (they WILL get the job done). And use Magic for emergencies and/or coup de grace I. e. Lightning. Don't forget to repoisoning your weapons as you fight.

Almost there:
Now you're an Adept Assassin, Expert Alchemist, Expert Rogue (Hiding), Adept Fencer, Adept Warrior, and (probably) still Journeyman Mage.

Now you will really start to feel the power of an Assassin. First of all, you'll be able to make Greater Poisons, and do Professional Poisoning, so I would recommend to cut down on adventuring and stay in town more than usual.

Rules of Professional Poisoning:
Never, NEVER cheat your customers. They will give you their weapons to poison those. NEVER cheat a customer of his weapon.
Always, ALWAYS apply a Strong dose of poison. Even if it takes you ten tries (not very likely) and you lose money, still always apply a Strong dose.
Obviously you should never sell poisoned food, as you will get flagged criminal if it poisons somebody.
Prices for poisoning with Greater poison will vary between 50 and 75 gold per Weapon (not per attempt).

Your main goal now is to become a Master Assassin AND a Master Alchemist, so grind, grind, grind. Make Greater Heals for additional Income and Skill gain.

Action wise you should take on any medium strength non-magical monster with no trouble at all, be it an Ettin, a Troll or an Orc Lord. Always be careful with magical monsters and don't forget that you have some magical abilities yourself to rely on. Greater Poison works very well.

As a Master:
Master Assassin, Master Alchemist, Adept Rogue (Hiding), Adept Fencer, Adept Warrior, Expert Mage.

After 95 skill in Alchemy you will be able to produce Deadly Poisons with a reasonable amount of success. This is it, this is the top. You are an accomplished Assassin and Alchemist. Yes, you can become Grandmaster in both skills, but that won't change much. As a Master you will receive almost all the benefits of a Grandmaster except for the Title and little more success when brewing Deadly poison.

By now you will have a customer base, and will probably be in a guild (the larger the better). Just keep doing what you did before only this time with the Deadly Poison. Deadly Poison opens a whole new horizon for an Assassin. It can kill the toughest melee monsters (including Ogre Lords, Wyverns, Cyclops, Drakes, and Ophidian Avengers) in a matter of a few seconds. Just run up to them, inflict poison and run away. The poison will do the rest. Now you can also dabble into the art of human assassination and be rather efficient at it. Again, poison will give you an edge against Warriors, Archers and Mages. If you're careful enough you'll come out ahead most of the time. Business wise you can now Poison weapon with Deadly Poison for a fee of about 250-300 gold per weapon, you can also sell various potions for some extra income.In other words you are on your merry way towards the Grandmaster. Enjoy the road!