RESIST: 
0-~45Resist: Ok you are at 20% resist now and need to build it up, look 
for an bone magician at the britain graveyard and go stand next to him. 
Having some skill in healing helps alot too. just sit next to it and try 
not to hit it. When you run out of hitpoints open the first doors and go 
outside to heal yourself, close the doors on your way out. Alternative 
way is to get a friend who is nice enough and tell him to shoot magic 
missiles at you. Gains easily to 30+. after that it might be bit hard 
with fireballs but it works. 

45~55 Resist: Go to Vesper graveyard and lure 1 bone warlock behind the 
fence. Remember you need high enough healing% or bunch of cure potions 
to train with them. Again just sit next to it and let it blast. A harm 
spell from a blayer with ~45-60 evalint works here nicely too. 

55-~60 Resist: Do the same thing than before, but this time lure 
2 bone warlocks and train with them. Alternative choise is to pick 
up an friend whos training magery and make him to summon water elementals 
for you 
Lightning spell from a player with 45-60 

ok.. here comes the painfull part. I myself hated it and it was way too slow. 

60-~75 resist: I continued training with bone warlocks, 
i lured third one to blast me (sometimes third spawns). 
I trained with them up to around ~65ish resist. It took 
_LONG_ time for me to get any gains so id suggest on 
finding an better way. I think that finding an sister 
which summons alot fire elementals would be a good 
option to do this. Or just find wilf fire/air elementals to blast you. 

~75-90 resist: ok this is the easy part. First at ~75's go 
to the ice cavern bit north from wrong and first lure from 
one to two ice elementals to cave entrance. Let them blast 
you and when you are down to under half hps go out of the 
cave and heal yourself up. And be sure to use resist stuff 
like royal ore armour/vampire bone add ons etc. And few 
strength jewels wouldnt do bad either. After you ding 
close to ~80's you better lure 1 or 2 more ice elementals 
to the entrance, I myself trained with 4 ice elementals 
at the same time. The highest spell they cast is the energy 
bolt which doesent do much. But be aware, surprises may occur. 
4 energy bolts at the same time might kill you. This allso 
needs high healing skill to work efficiently enough ( i had 85). 

90-100 resist: OK i havent reached this spot yet but this is what i've heard. 
You still should stay in ice cavern, You need HIGH healing to do this 
efficiently and gheals too. Remember Anything might give gains. Since 
ice elementals have pretty high eval they are good to train, and they 
shoot alot of them minor spells. You could perhaps try some 
lich lords/daemons and so on. Just remember to carry enough 
healing power with you. 

Remember patiency is the key. 

HEALING: 

Healing: 0-55 Spar with lesser monsters without armours and heal yourself.. 
at 0-20 skill youll be only able to heal yourself when you have lost max 
10% of your health. at 20-40 you can heal yourself up to 25% lost at 50% 
youll be able to heal you nearly from 50% health. 

Healing 55%-65%: This is the time to start to play a bit with poisons, 
you can either get ~200-300 lesser poisons which do not cost much or 
find some animal which causes lesser poisons (normal snakes i think.) 

65-~75 Move on to harder poisoning monsters like spiders and giant serpents 
(giant serpents might prove very fatal). Or buy an bunch of normal potions 
and drink them at healers hut. By curing youll get good gains. 
(you can allso try at 75% to get yourself to ~10% life and start healing 
from there, this allso gives great gains) 

75-80 Get yourself to as low life as you can and heal yourself 
(by drinking poisons and curing yourself in low life works fine) 

80-90 Its time to move to bucanneers den and start doing the hard part. 
Id suggest to do like this: Clear every possible monster 
(including necros/pirates/sisters) about ~100 tiles around the healers hut. 
Leave only 1 giant serpent alive. AFter you do that, make sure you are 
carrying greater cures with you. Drag the giant serpent to the other side 
of shore where the healer locates and use the bridge on the left to cross 
the shore. Go next to the giant serpent and right after it has poisoned you, 
Run to the corner of the hut and cure yourself. Just be sure that the serpent 
doesent follow you pass the bridge. 

90-GM 

Get yourself an necromancer friend who needs training. 
(you must figure this out by yourself)