My advice is to use the enviornment to your advantage. If you see crates lay a Claymore around the side of them so they don't see it until it's too late; people won't run towards something they see. The best map without a doubt is Warlord in the Special Forces expansion. Be SAS and go cap the 3rd Floor of the Palace at the begining of the round, but lay some Claymores around some corners so if someone decides to run in and try to save the cap, Boom! If you're lucky you'll get some nice Palace battles going on in which you can get 10-12 kills per battle. One side will eventually take the other over, but don't fret. The other side will always come back and take a flag back. This is how I got my Veteran and Expert.
Expert Explosives Ordinance:

Yes, I wasn't in the Palace, but soon my young Padawan you will learn the ways of the Clays and you too will truely be an Explosives Expert.