Untill you reach level 20 you really only have two major attacks. Vampiric touch and Windstrike.
While soloing try to stick to hunting creatures that fly, ie. imps, bats, succubus, etc., they all have a weakness to wind attacks. Wind strike consumes less MP than Vampiric touch and does better damage at lower levels.

Avoid hunting Zombies and Golems as they have a high defense against magic attacks and it will take over half you MP to kill one of them most of the time.

Dont waste skill points. Armor Mastery is one you should skip unless you really need it. At level 20 you stop getting this skill and get either robe mastery or light armor mastery. These are worth taking. But at low levels you can increase your defense easier with a cheap shield and save your skill points for when you reach 20.

Dont take Cure poison untill you reach 18. This is when you'll start encountering more mobs (arachnid trackers, poison spiders, sucubbus)that can poison you so its worthless untill then.

Anti magic increases your magic defense by 3, so if you find yourself with a little extra adena save your SP and get a Necklace of Magic which will increase it by 15.

Save your adena. Compare the cost vs. the increase. For example a Necklace of Magic gives an MP def increase of 15 and costs around 60 adena, now a Necklace of Knowledge gives a MP def increase of 18 and cost around 1,100 adena. Thats over 1,000 adena for only a +3 MP def increase.So unless your trying to get a set bonus (ie. Tunic of devotion set) save your adena for when you reach your 20's where youll be keeping the same equipment for more than a couple of levels.

Spiritshot. As soon as you can afford them buy a bundle of these. They make the difference between a 1 to 2 shot kill and a bunch of down time.

Dont do the Scent of Death quest unless plan on duoing or grouping for it. The quests entails you defeating zombies and is not very rewarding. It will take you longer to do this quest solo than its worth, since as I said above, Zombies are powerfull against magic attacks.

Dont buy the first D grade equipment you can untill your sure its what you want. If you are in no grade at level 22 its fine. Its better to save for a set youll want to keep for a while as things just became a whole lot more expensive.

Hope these help and I'll be adding more as they come.