Three basic tips can help you get started. 

First, even if you are an experienced HEV suit user, 
you should avail yourself of the Hazard Course. It 
teaches you how to use the suit (the equivalent of 
armor in other games) to its fullest advantage, and
that special long jump module could save your life. 

Second, as Black Mesa deals with a wide variety of
"special" experiments, it is important to remember 
that many useful items are stored in the plethora of
wooden crates and containers throughout the lab. 
Smash 'em all and look inside-but avoid the ones 
marked "Explosives" if you know what's good for you. 

Third, remember that the guards and scientists are
your friends; they can watch your back, heal you, 
and even get you out of a sticky situation. Often,
if one dies, you cannot continue. Save early and
often.