Avoid spending too much on one thing.
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.
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.
Make sure furniture decor has similar scale. It's all about scale, proportion, measuring, being conscious of the overall plan.