Here are some of the basic things that I tell anyone that enters the site for the first time.
If you're completely new to making music (no composition experience whatsoever), I would suggest directly copying off of songs you'd like to start composing in the direction of. Doing this practice helps develop musical literacy, which then serve as your fundamental building blocks for whatever you decide to make in the future.
In order to make plausible music, it's really important to develop an active ear. You should work towards being able to distinguish different instruments inside of a simple song—or develop the ability to hear different notes in a chord, for example.
I also want to dispel this from the get go—music theory is not a requirement to make good music, nor is knowing how to read sheet music! While these skills are helpful to have to some degree, ultimately, these serve as a means of standard notation that don't actually hinder your potential ability to make music.
I've also seen a lot of people who want to make music for games, but they seem to be learning how to make music in a rush. I think the most important tip of all is to not be disappointed in yourself if your music comes out cruddy even after 6 months. If you're starting completely from scratch, music does have a high learning curve—but it should get easier the more you dedicate your day towards making it and fiddling around with things.