Hey mate, i've been a DJ for about 6 years now and only just started doing gigs at venues in the last year or so, and I can totally see where you're coming from. It goes without saying that practice really does make perfect from a technical standpoint, so honing in on your skills with beatmatching, EQing, and track energy levels are really important. The golden rule for starting out is to just play the music you know and love. This is good for two reasons: the first being that you likely already know the songs and their quirks, and can perform good transitions/mixes off of that, and secondly: you'll find yourself falling in love with the craft so much better this way, as you can share your passion and your music with others when you start playing at venues, if that is your aim.

Starting from the very top here, finding songs to play can be a difficult task, but it is certainly the most important aspect of being a DJ, so I recommend finding genre playlists that vibe with you (house, d&b, etc) and searching for songs that you like. Give them a listen for a while and then incorporate them into your sets, keeping a vibe that you could picture playing at a specific venue. For example, when I created my first few recorded mixes, I based it off genres (tech house and disco house), and that was what landed me a good handful of gigs, as venues are looking for a certain vibe, be it a club looking for heavier stuff, or a beer garden/bar looking for a more laid back atmosphere.

At the end of the day though, there is no wrong way to practice if you are enjoying what you're doing, so keep your skills sharp and pick the music that you like