Note! I take no credit for these trick or glitches what evah!
You won't get banned for doing these!
Third tip may be pretty useless.

First tip
What it does?
-You can see enemy stealh bombers.
1. Go to options
2. Turn color blind on
3. Vola! You can see enemy stealh bombers if you look at mini map

Second tip
What it does?
-More fire rate for your CM901 assault rifle.
which makes it's damage better
1. Get CM901 Note! You must be level 18
2. Get your CM901 to level 8
3. Put grenade launcher in it
4. Vola! Your CM901 shoots faster

Third tip
What it does?
-You earn your double exp from specialist package.
1. Just take only one perk from specialist package
2. Then kill somebody
3. Vola! Double exp
EDIT. Of course if you use Hardline you
need only 1 kill to get that first perk!

Fourth tip
What it does?
-You get Sitrep Pro faster.
1. Put sitrep as your third perk
2. Put trophy system on the ground
3. Knife it
4. Vola! You get sitrep every time you knife it

Thanks.