The advice I always give people is this:
1.) Practice, practice, practice. It took me years to get to where I am. But don't be discouraged; it will be worthwhile to see how far you've come :)
2.) Come out of your comfort zone. I used to only draw girls. ONLY. But it is because of something I challenged myself to do once that I am now much more confident in my ability to draw boys. And don't be scared that it won't turn out well. Just try your best, and hopefully it will open a new ability in you. And if not, that's fine. Things take time, so don't be discouraged if it doesn't work out the way you wanted it to the first time around.
3.) Try out what you see. Ever look at someone else's art and think, "I really like that eye style"? Well, try it! Don't think of it as copying, but as inspiration.
4.) Be confident! I used to draw... looking back... not so great. But back then, I believed my drawing was awesome, and because of this I had the motivation and confidence to keep on drawing.
I hope this advice will help you! Always do your best, and don't listen to haters!