Hello Sux,
the people in this Thread are not very friendly to you, they think you are a faker, because you have the same problem then i have. My English is also not the best.
Your Question is really not easy, i must give you very very long answers. I dont think that my English is good enough and i hope you can understand the following text´s.
Versus a Dexer you must cast Reactive Armor before the Duell starts. Then you must look which kind of Weapon the Dexer is using. If he use a 2-handed Weapon, you must Cast Poison, because he can´t cure with this kind of weapons. You must also look if the Dexer has balanced stats or not. When he has no balance, then you can lower his Intelligence and always use Mindblasts. If he has balanced stats, then it´s better you use a big Combo like weaken/Explo/Flamestrike/E-bolt....something like that. Often use Poison from a near Distance to the Fighter, because you are Poisoner.
Against a Mage you must also look at the stats. If the Mage is unbalanced, you must use Clumsy/Poison/Mindblast Combos. If he is balanced, then it´s better to do it with large Spells like e-bolt´s/Poison/Weaken Combo´s. You must disturb his Cure with a quick Clumsy casting. That´s not easy, but you must try it everytime. If the Mage is attacking you, always look at your Healthbar. You must cast the small Heal often and very quick. Normally the other Mage use Poison against you, that you cant Heal yourselfe. It´s very important to Cure yourselfe quickly. If the mana from your opponent is low, then you can start the next attack.
I hope that another UO-Player can give you answers in a better English.
good luck,
trini