Think of how much furniture you need. What's the best way to have it be functional in a great way? If it's in groups, define it.
Be judicious with your budget and buy things that are going to last.
People buy things in isolation and don't think of how they work together.
To have a 9-foot sofa in a small room can be kind of treacherous.
Avoid too much intense color. Make sure you mix colors and try them out. It's always good to do a swatch.
Look at your world and your life, and look at what is personal to you. If you're living in an apartment, you need to stick with a narrative that's personal to you.