1 - Don't try to sound like someone else. It's inevitable that everyone's music will resemble someone else's. We are all influenced by what we listen to, but to try to sound like another musician is not going to help you stand out. Just be true to the sounds you want to make. Eventually, your own sound will emerge.
2 - Write a melody you can sing. This rule can be broken, of course, especially with more ambient styles, but generally the memorable melodies are the ones you can sing without being an opera performer. If the song gets stuck in your head and you still like it, you're probably on the right track.
3 - Think horizontally more than vertically. If you're a nerd like me, you sometimes think more about the techniques of writing music rather than the end product. In other words, if you're more interested in using a certain chord structure or voicing, that can cause you to get stuck thinking only about the vertical. You need to think about the horizontal arch of your piece way more than the one cool chord you are dying to use.
4 - Make several versions of the same piece. Let's say you have an opening phrase that (as Miles Finch would say) you're totally psyched about. Then you have to write the next musical phrase and maybe it's not as great. This is a perfect place to try out several different directions. You know you want to keep the first bit, but you aren't sure if the next part works. Just make several versions and go with the one you like the most after a few days. You can also try just varying the tempo or even the meter.
5 - Be willing to start over. It's really hard to delete something you've written, especially if you've spent hours on it. But sometimes, the delete button is your best friend. I've worked on pieces for hour and hours only to finally admit to myself that it's just not working. Much of my first album makes me feel like that now. I should have been willing to axe parts that weren't working or whole songs even.
I hope these tips are helpful. Whatever happens, don't give up. Your music can have the power to change someone's day. Happy writing!