I noticed on JD's 1996 What Up Doe Sessions he would sort of lower the volume on the sample and bring it back up and I had never thought of doing anything like that before....but yeah, what are some of the things you guys do?
what you're referring to is actually not the volume of the sample being turned up and down, but a low pass EQ filter on the sample being turned down to like 100-200 Hz (where the bass frequencies usually lie) and then turning it back up to like 10Khz (where the highs and mids lie)...sorry if that sounds too technical, but this is the lingo you've gotta learn if you wanna step your game up. it takes a lot of practice and failure haha-- coming from someone who's failed way more times than succeeded.
but if you notice your favorite producers' beats, you'll realize that the one thing they all have in common is professional or at the very least semi-profesional quality of their mixes...and that takes time to learn. i recommend watching YouTube tutorials and stuff to try and figure out the quirks of whatever system you're using to create beats, but as far as "keeping people interested" that's sort of another story.
things like variations on your patterns, even subtle shit like vocal cuts or sound snippets, are things that do get noticed by listeners, and the more you switch shit up bar-to-bar the more likely someone will stick around the whole way through. also, on a last note, don't stretch your beat to 3, 4, 5 minutes if it's just a 4-8 bar loop...nobody wants to hear that shit anymore haha; unless you can somehow justify the song length, i would highly recommend trimming those beats down to like 1-2 mins. i know if a song is like 4 minutes, i'll usually just skip right over it before even checking it out-- but maybe that's just me. anyway, hope all that ^ helps.