I think that, besides the great things mentioned above it's also very important to have certain arranging techniques which are difficult to acquire by yourself. This of course depends on the genre of music you're writing, but a good knowledge of things like voice leading, instrumentation, reharmonization and similar things are generally very useful and help a lot with composing. Luckily, there are a lot of books about this. I'm personally not a big fan of books, but there are a few classics out there which in my opinion are a must have for every composer. Of course, it's a totally different thing whether you're writing for a string orchestra or for a rock band, so I can't really recommend anything as I don't know what your type of music and line up is. But, what I'm trying to say is that you don't have to do anything by yourself. There's a lot of people in the world that know a lot about composition and are sharing their knowledge in great detail for a small price.
Just blindly listening to other people and constantly staying in a safe zone is of course also not the way. Absorbing information about things that interest you, and meanwhile experimenting with the things you're learning is in my opinion one of the richest and most fulfilling aspects of writing music. It's about the joy of discovering. Just playing around with chords on a piano for a few hours can be a very valuable and educational experience. This, in my experience, also brings the best results. Someone can tell you that the first inversion of a major chord sounds amazing, but hearing it yourself, and most importantly, stumbling on it by yourself when you're just messing around a bit, maybe accidentally adding a 9, has a lot more impact. First of all because it highly depends on the context, but also because that way it comes from yourself. This makes your music more you, and this authenticity and personality is what makes music so beautiful.