pro tips: play in a full party and travel in pairs. One guy covering the other.
If you are going to rush get two people to cover you and plant it as soon as possible.
If you are going to camp, Make sure you have teammates blocking off the flanking routes.
If you are going to play by your self, patrol a section of the map and pay attention to the skulls on the screen (signals that teammates/randoms have been killed), so you can prepare yourself for approaching enemies.
^just some general advice.
Custom class and combination with above tactics.
SnD Class #1
Primary: Mp7 (Extended mags w/ Focus Proficiency) [A generally good gun. Don't need to worry about reloading because of the extended mags, and the silencer isn't necessary IMO, as long as you can be aware of the surroundings. Use Focus to win any gunfight that you get into- Goes with most strategies {E.G. Rushing, Patrolling, Planting}
Secondary: P99 (Extended mags)-[In that weird case, where you run out of bullets in your huge magazine, Switch to your secondary to finish your opponent off, instead of taking a lengthy 3 seconds to reload]
Lethal: C4 [Combos with Quickdraw. Use when you need to take care of a camper, or someone who is out of direct view. Good for handling crowds]
Tactical: Flashbangs [Use these to paint your enemies with recon, and as a preemptive strike on the enemy.
Perk 1: Recon Pro [Help out you and your mates by spawn-nading the other team. Be wary of dead silence users though. Also, in the off chance that you die in a gunfight, you can have your murderer (?) painted on the map for approximately 10 seconds.)
Perk 2: Quickdraw Pro (Pro is a must) [Aim into the gunfight faster than the opponent ever will. {standard ADS time for a sub machine gun is .2 seconds, with Quickdraw it's .1} Throw your flash grenades and c4 a little faster to let you fight more.)
Perk 3: Stalker Pro (My favorite perk. You can absolutely destroy the opponent in any gunfight, while using focus and stalker. The Pro version of Stalkre also keeps you safe from claymores, betties etc.)
Hope I helped a bit.