Drawing from life is the most common but practice and perseverance are the key to what ever method you choose. The reason for this is simple: life has the lines, gradations, colors, angles, negative shapes, patterns, textures, and other material you'll need to practice every time you look at it, whereas your imagination can not hold anything nearly as complex as the most simple reality in place without years of training. Experience is the most important factor. And it is one that you can only gain from practice, from perseverance, and reference.
Adopting a style is fine, but if you forgo understanding the basics you're going to hit the same wall every time-- not to mention only be able to draw your style.
A style should be more something that happens as you go along, after gaining an extensive understanding of reality.
If you see a weakness in your drawings push yourself to correct the mistakes that you see. Don't accept them, but work to change the way you work.
For me, it has always been a chance to explore areas that I am not comfortable with. And in so doing I am able to make improvements elsewhere as well. One thing that has improved my skills has been my willingness to use reference. I've always found drawing using references to be invaluable, you cant just expect to create a perfectly proportioned image from your mind. This is equally true even when trying to create fantastical or fictional creatures. Many fantasy artists base the anatomy of their creations on real world creatures, this gives them access to real
Improvement is easy if you are willing to go and work for it.
You're going to need to tear down old habits and build new ones in their place, accommodate the messiness and mistakes so you can get around to correcting them in the same drawing, and take a lot of criticism to make great art (showing us your work is a great way to help us help you).
Don't stop and don't forget to keep your goals in mind.
Don't just discard your failed attempts, I have always found it useful to go back and look at my past work. What would I change, what would I do again. Try to learn from them because they can be valuable in a lot of different ways. If you're using a reference don't just look at it. Try laying the drawing over the reference and trace the original so you can see your mistakes.
Don't be afraid to experiment, keep drawing and you will improve every time you pick up the pencil/brush/stylus.