Getting Started:
First of all you need to get some runes. One way is to rune craft or just buy them and then when you have a reasonable amount of each then it is time to buy stuff.
- Air staff: These are the best for beginners magic.
- Fire staff: Use these later.
Where To Go
Now lets find some spots. I would suggest for a mage level 1-10 attack goblins and then scorpions from the top of al kharid mines until around level 25 mage. At this level I would attack the lesser demons in the wizard's tower, as they cannot fight back and you get good experience.
What Spells To Use
Lets start with air attack until you are a higher level and you can do better spells. I like alchemy but it's a waste of runes really, as you progress you can shoot through the mage levels.
Runes are expensive and rune crafting takes along time. I would wait until you get your level up and you are earning more GP before you explore your mage power as this could bankrupt you. For instance, I had full adamant about 30k and a load of cool stuff, then I started mage and lost it all.
Have a nice game!