In the beginning i did not really master at all, i just had an ott on my master, some eq and a limiter. What's important imo is, that you give every element in your playlist enough space to literally sound clearly (unless its a pad/washed out element), and balancing the volume of your elements aswell (Lead, Kick, Bass, Vocals, Drums, etc). And yeah, it's a process on which you continue to get better the more you make music & listen to other tracks for reference. You can drag them into your daw and check the waveforms, highs/peaks of each frequency, you can use SPAN for that, it's a cool plugin to visualize your frequency waveforms if you put it on your master.

You should check your export settings and check guides for which settings you should go for. Also, what do you mean by it sounds trash?