Listen to a fuckload of music and not for pleasure. Really study and pay attention to what's going on in professional productions. Try to emulate them. Don't fall for all of the courses and cheat sheets that claim to give you universal solutions to mix downs. The truth is that there's no exact science or flow chart for a tight mix. Assuming you build every track from the ground up, it's always a constant struggle to get everything working properly. Yeah just listen to obsessive amounts of music. Everybody in the thread will tell you to just keep failing, which is completely true, but you should also study music very intently and try to do whatever you've heard that works. Unlike composing which is a pure art, mixing is a craft that will only yield results through self-teaching. Aside from very specific situations, mixing really isn't something that can be taught outright.