The very first thing I do whenever I move into a new place is get things on the wall. Floating shelves and framed pictures especially. I usually just buy cheap frames that I think look good.
Without exception, people normally comment that the place looks lived in despite there being boxes all over the place. The trick, as I've found, is to make your home look the way you want. It's your space, and if it's your space you can decorate it how you like and it can't be "wrong". The decorating style speaks to your style and your own flairs and personality will come through. Do what's pleasing to your eye.
Personally, knick-knacks and some books, old DVDs of favorite movies, travel (or other) mementos, and small plants on the shelves seal the deal for me. For pictures and other framed pieces, my aesthetic leans towards semi-chaos looking. No neat rows and columns on the wall. I just throw things up and move them around as I see fit.
Don't sweat the details, there is no "wrong" when it comes to personal preference for your living space. Make some tiny holes in the wall for your "pieces of flair" and don't worry, they can be fixed or filled in as needed.
If that's all still too much, get some houseplants and spread them around your home.