Is there something that you want to illustrate, but feel like you can't? Maybe it's faces or people or a certain animal or flowers. You shouldn't feel limited to drawing only what you're comfortable with. The fun in art is growth, and if you really want to draw something you have to learn how to!
To do this all you need to do is dedicate time to doing studies. Study your subject many times by doing quick, realistic sketches (focus on your problem areas) and then try illustrating it again in your own style. I guarantee you will see instant results. You must continue drawing it constantly, and over time it will become effortless! But, you have to put the time in to see results, effort is the secret ingredient!
Don't hold yourself back from drawing what you love! Just put the time in and watch your skills blossom!!! ;)
For example, I always wanted to be able to draw crystals with minimal references. So what did I do? I learned the subject super well, did a lot of research and studies, and understood it so well that I made a class on it! Now I can put my own twist on the subject with minimal effort and keep it believable!
Just remember that everyone out there that draws anything well put the time in! It's not some magical talent they were born with. It's just practice and perseverance!! :)