If you really want to be effective in gaining XP in Domination when you play solo, especially in smaller maps then:
Play objective but only keep two flags at a time
Jumping on one if another team-mate is capturing it though so you get the points
For the rest of the game camp on B flag to gain defend points and only push off of the flag when the rest of your team has pushed them into their spawn temporarily.
If you can keep them in a spawn trap go for that and get offence kills.

Go for spawn grenade kills whenever you can since they're very effective and they're easy to get used to using correctly and if you're getting spawn trapped when you join a game you can take the same approach by sitting on your own flag and getting defend points that way.

Use your preferred gun with Juggernaut/Stopping power, Martyrdom (if you rush) or Deep Impact and finally Bandoiler/Fragx3 with a RPG class in case you're against a good team that gets helis.

Would advise an AR such as the AK/M4/M16 for long range static players or the RPD for players who will happily boringly sit at a window all game.

For more active "rush" players I would advise MP5/AK74U(without silencer as it increases hip fire spread)/P90 or your preferred shotgun of the two (if the map is close quarters).

If you have a 4-6 man in DOM then take the 100 - 50 points in the first round then in the 2nd go 150 - 100 before letting them cap B flag then just before they overtake on score recap B flag or their spawn flag (If B is well covered). Try not to push spawns as well.