Some sound advice there, my 2p worth would be :-
1)short gun/wepons are far easier to move with.
2)get as big a mag as you can, mag changes *can* slow you down in a fast paced game, or allow your oposition to get the drop on you, unless you have uber skills ... i dont, thats why i love my mp5k's 2500 drum mag :wub:
3)you dont need high ROF, but i find that 14 - 17 bb's a sec is a nice ballance to weight of fire and ammo conservation.
4)LISTEN all the time, you can often hear someone strike a pyro and get into cover (thats why i have a BFG ... they make no sound till detonating), or if your being sneaky, you can hear people aproaching from distance.
5)shadows are your friend, you can hide easliy and be all sneaky and ninja

h34r:
6)aviod doorways as much as you can, or cross them quickly.
7)be as small a target as possiable, look at how you stand in a mirror
8)stand back from windows if shooting out of them, it makes you harder to see.
9)often flee'ing or drawing the oposition into a trap is a good thing
10)avoid being lulled into a false sense of security (see point 9)
11)corners and doors ... thats where the danger is
12)Knee pads!
13)keep your load out minimal ... nothing worse then being loaded down with junk, or with a chest rig thats restrictive etc.