Black Ops, like most CoDs (all the ones I've played), can be variably frustrating depending on
-How good your connection is,
-How persistent you are to use strategies that are fun for you despite their ineffectiveness in comparison to other methods, and
-How much a perceived videogame wrong can effect you as it piles and piles on.
For the most part, just slow down and don't sprint if you think there may be an enemy. Know and respect the enemy spawn hive. If you're still having consistent problems, you're either playing on nuke town or the enemy has found the better of you (a head-to-head battle is a two-way street, it might be the enemy more than it is you in a particular situation).
-How good your connection is,
-How persistent you are to use strategies that are fun for you despite their ineffectiveness in comparison to other methods, and
-How much a perceived videogame wrong can effect you as it piles and piles on.
For the most part, just slow down and don't sprint if you think there may be an enemy. Know and respect the enemy spawn hive. If you're still having consistent problems, you're either playing on nuke town or the enemy has found the better of you (a head-to-head battle is a two-way street, it might be the enemy more than it is you in a particular situation).