the best advice so far was from daelin and i'll add on. First of all, when you start out, your skills are going to be simple, plain, and probably not very exciting. Perhaps you might want to simply try making new skills from already existant ones to see how some spells work (this helps when you get better). Granted, the begining is usually a little boring, but the good part is as you make more and more (and snoop around the spells section to find some new tricks on how stuff is done) you're spells will gradually increase and become better.
You already have an advantage a lot of spell makers didn't. Version 1.17 of the map editor, which has a lot of extras the previous ones did not.
So your first thing to do is make as many creative spells as you can in the editor alone without triggers. Try and mimic spells you've played with in other video games and the like. Try to combine spells for different effects and see with you come up with. It's pretty nifty what you can make if you try. Once you've had some practice with spells and learnt how they work it's time to move on.
Second line of business is starting off with triggers. Now when you first see peoples triggers, you might be baffled, maybe not but play around with them to see what they do. Eventually as you learn the basics, you'll all-of-the-sudden have a new field of spells you can make. When you start making more complex triggers, it's best to test one thing once to make sure it works before moving on. Then you learn how to use more and more specific functions (like the use of vairables, arrays, and other stuff such as dummy casters) functions until you've mastered all the functions and are able to make full spells testing only the finished product.
This is the stage i'm at since i;ve never bothered to learn JASS but i find there are very few spells i cannot do with triggers.
Now JASS is the highest level of game editing. This is where you can really change stuff up way more than triggers or basic map editing. Although most spells can be done effectively via triggers, JASS is mostly for custom systems. Check in the JASS secton and you'll find a whole bunch of systems that are used to change the gaming dynamics, or simply solve some irritable problems. I really haven't tried using JASS but i've heard it takes a while to master, but is far better once you do figure it out. If you take a look at the difference it's quite astonishing.
Anyways, these are the three levels that you go through and you seem to just be starting level 1. So follow these tips and everyone elses and you should eventually be able to make great spells.
Remember, this is NOT just changing some numbers. If you think it like that, then i'm not sure if you'll get too far into triggers or even past making interesting spells.