This is totally a guess, but if you don’t want the background noise, maybe record from a lower angle not high up, you move closer towards the sound object and record from below, but I’m making this up, I believe you will hear more things and background when you record from above and put the mic higher up, so proximity and angle important (maybe you should do some cardio before this )
I would choose to record sounds that you find interesting when you hear outside of music (if you don’t have a song or project yet in mind) you have to enjoy the feeling of a sound, that is the one that will lead to your choice, otherwise its really subjective. For example I like the sound of trains so I would enjoy recording that. However if you have a song or theme in mind then you may not record a train, but let your natural enjoyment of sounds guide you to one. I used to record people talking in my family , so all their secrets are documented now, but I think I may have lost this tape unfortunately. Looking back I realized since i was a kid I did not like anything to be quiet… so that’s why I would record things to play them back for myself.