Looks good for just starting out. I'm sure the bettered skilled mappers here will have all the answers you need. And it's 1000% better then my first feeble attempt at using GIMP for this style of map.
I feel that the mountains came out well. The one thing that really catches my eye is that the forest look like they are just plopped down on top of the land. Your mountains blend in with the land and the forest doesn't. I don't know how to fix it, but I'm sure it will be explained shortly. And I can use that knowledge to improve myself.
I think its a wonderful start, can't wait to see your island progress.