1. Uniqueness lasts
It can take a while to find your artistic style and vision, but when you do find something that makes you unique, hold on to it. Take time to develop your works and make sure they all showcase something that is unique to you. If you try to imitate what's popular, you may well experience some success, but it will likely be short-term success because something else will be popular in a few years' time. The key to long-term success is to always be unique because your uniqueness will last, whereas what's popular now might not last as long.
2. Everyone gets rejected
Rejection is something you definitely have to be prepared for as an artist. It's pretty much guaranteed that you will experience rejection at some point or other. When you do get rejected, what you have to do is to pick yourself up and put it behind you; move on to whatever's next and keep trying to get to where you want to get. If one door closes, there are still plenty of others that are open. Rejection may well in fact lead to something great.
3. Continue soaking up knowledge
You're not going to learn everything about art straight away. Art is a fascinating and extraordinarily rich subject with lots of branches. Be prepared to learn new things as you progress. The more you learn, the more you'll be able to appreciate other works of art, as well as your own. The piece you've just finished may be very different to the piece you did five years ago because all the knowledge about art you've soaked up has influenced your creative process. You may well want to push ahead with your own style, but don't be afraid to learn more about art, as it can greatly benefit you.
4. Be committed to working hard
Creating art is something that requires a lot of hard work. To create a really great piece of art, you have to have a vision of what it will be and once you have that vision, you have to dedicate a lot of time and energy to realising this piece. It's very easy to start a piece and to leave it incomplete because you don't have the time or motivation to complete it. If you take the easy way out, you're not going to succeed. By all means if an artwork isn't turning out how you want it to, move on to something else, but don't give up on something just because you haven't got the time or motivation. A good artist will find the time and will be motivated enough to complete their works.