I can sum up my x.p. style in saying that players earn x.p. You have to do something to get it, it's not yours by merit of just showing up at the table. I reward participation and effort.
I give out individual x.p. awards, generally based on what the characters actually do over the course of a session (not necessarily "achieve," I'm looking for basic interaction and effort). The big reason is to give players an incentive to participate in the session. I'm just tired of seeing players that show up and bury their noses in a smartphone/laptop/comic book/whatever and roll dice when prompted. I've tried having discussions about this, but the only method I've ever seen that consistently makes people pay attention to what's going on in the game is to only grant the characters x.p. for encounters/challenges they participate in. Have your rogue hang back instead of checking for traps? Fine, but the fighter at the front of the party that blunders into the trap gets the x.p. for finding and surviving it.
Absent characters generally get no x.p. Since I'm adjusting the encounters to compensate for the absence of the character, it's perfectly fair to adjust the amount of x.p. that goes out as well. There's also a world of difference between a player that gets stuck at work or with family issues than someone who misses the game because it's just not a priority for them... Someone that misses a game or is late because of unavoidable situations or "real life" sometimes gets x.p. Since everyone has one of these moments every now and then, it's common for a player to miss about one session out of every six or seven in my experience, and it evens out over time.
I don't give awards for roleplaying. It's a roleplaying game, so I assume that's going to happen. If by "roleplaying" you mean social interaction... I consider social challenges a type of encounter and award experience accordingly. Describing your character's heraldry? Not really x.p. worthy, that's something you should do as part and parcel of designing your character. Convincing the duke to send troops to defend an important mountain pass? That's an encounter really, it just doesn't involve initiative and attack rolls--definitely worth some x.p.
I also don't give x.p. awards for backgrounds. I expect a certain amount of this to happen by merit of the game's nature. I also don't feel that the character's past should be as cool as what they are doing right now, and I don't want to read novellas for first-level characters. I'm happy with half a page (or less) that includes a basic explanation of the character's family situation, how they got their class skills, why they decided to become an adventurer, and at least two "loose ends" that I can exploit for future adventures. The reward that you get for writing a background is in seeing that background incorporated into the ongoing game.
For things like people bringing sodas to share, hosting the game and so forth, I give out one re-roll during the session. That encourages people to do it on a regular basis without skewing the experience progression.
I award x.p. during the week, between sessions, and send them out through email. Players handle leveling up on their own time, away from the table. Sometimes I use training rules, but most of the time I just require a player to explain why they got new abilities that aren't directly related to the game's narrative. A fighter wants to take a level of cleric? Why? Did you have a religious experience? Barbarian? Why? Does your character have anger issues or something? Wizard? Why? What order of wizards accepted and trained you?