The advent of YouTube has truly revolutionized not only the way we can learn a new song, but gives us the opportunity to hear many versions of a song too, often in in many differing styles and tempos, opening up ideas to possibly expand & take it further as well. You can then find the lyrics (and possibly the chords) by doing a simple Google search. I wouldn't completely rely on this for accuracy though because the the hit cover version chords & lyrics often differ. That said, if your goal is to emulate the recorded version, it's critical to rely on your (trained?) ear to actively listen to the YouTube recording and be able to identify the actual chord progression & bassline played, as well as memorize the actual lyrics sung on the recording.

I agree with Zuki that while some tunes can be easily picked up on first or second listen, others are far more challenging and may require going back several times, and in subsequent practice sessions to eventually master. There's something about 'giving it a rest' and calling them up latter (the next day/week) and discovering how much easier & quicker it takes to get under your belt then.

As far as choosing an appropriate style, the most fun for me is exploring alternative rhythm styles and different new chords for a given tune, when wanting to make the song uniquely your own.

When I save a song in my keyboard (aka Registration Set), like zuki, I too like to group it together with songs of a similar style genre, artist, or with other compatible themed songs to form a medley set.

Though I'm not as diligent & disiplined as Gary in making myself learn a new song every week, I do regularly rotate my core repertoire in attempt to keep them all (300+) polished, and also scout out new song possibilities (YouTube, Spotify, Billboard website, etc) and try to learn the ones that I think both myself and my audiences would enjoy.

Realizing how we all do it differently, I'm anxious to hear from others here on this topic as well. - Scott