There's definitely a knack to using them.
The style used by BT and others have a variable sensitivity probe - so you can use it on high sensitivity for finding stuff, and then turn it down as you narrow in on the individual cable/pair, and right down as you get to the contact stage. But because you do get crosstalk, for a positive ID you need to short out the pair to show that the signal goes away.
If you put the generator across a pair, or across core and screen of a coax, then it's not good for tracing a cable - by design these cables are low leakage. It's better to put the generator between one wire of a pair/the screen of a coax and an earth so that the cable then acts like an aerial. When you think you've found the other end, move the generator to be across the pair/core & screen of the coax to double check. Downside of this method is that you have a lot more crosstalk, so will find the signal coupled to other cables, especially if they are bundled together for part of their run.