On the dynamic's of an R&B song, usually they have more dynamic's and more drops in the beat. Also instruments is somewhat the same, but not. (try and sing R&B to Missy Elliot type beats). Soothing sounds are usually used to, like piano's, most strings, organs, some brass, some percussions etc. R&B tends to let a song "breathe" more in term of dynamic's, and kicks are not as dominate as hip hop/rap unless your talking about an R&B/rap mixture. Anyways, I'm no 'expert' in making R&B tracks, but those are the very basics. If you envision a singer, they do not "flow on point", it's not repetitive in terms of octaves & the overall vocals. (not that all rappers are like this). Instead of making a beat, that's for hip hop, which usually doesn't have any if at all, harmonics's, you would be creating a beat that can have a little something for the rest of the sung harmonics. Don't know if I'm explaining it enough, or right for that matter. Of course different tracks require different things, and different artists sing different, but they can be used as guidelines. Of course, you don't want a 200bpm tempo for a R&B track, cause then it becomes a pop track lol, or techno haha. Change the beat up quite frequently because of how the singer sings. A lot of the songs out there, when a singer is about to hold a key, they drop the beat, and kick it back in in a second if you know what I mean... I would probably start with listening to the artist sing on other tracks, before actually lacing anything, and also probably melodies before drums.
Watch the effects much, don't use compression as much, or you'll smash the dynamics
