Are you trying to find something specific, or is this a general question?
One old trick is when you suspect a capacitor, jumper it with another capacitor of the same value. If things improve, then it may be the capacitor. But of course, this implies that the original capacitor is open or has lost capacitance, rather than shorted.
If you're getting paid by the hour, it's probably cheaper to just swap out the cap.
I once worked repairing video game PCB's, and when we'd get a really knotty problem that took too much time to diagnose with the scope, we'd "shotgun" it - just replace every chip on the board, because it was cheaper to take an hour to replace 20 or so chips at $0.30 apiece than to spend four hours troubleshooting at $30.00/hr.
And I've been in the business since 1968, and have never seen a capacitor tested in-circuit, let alone done it.
I posted a URL of what I use which works very well, I can tell you a basic theory of how it works. The in circuit uses the resistive load in the circuit to offset the reading from the test cycle on the capacitor. It's not perfect but it's very close for doing debug work. what I have found is this. In many cases where a cap test resulting in much higher value than should be, may indicate a leaky cap. Of course, one that test much lower is most likely a weak cap.
As far as doing repairs, I haven't yet pulled a cap from a board using this LCR meter that showed a below normal reading to be false.
I have seen where at times, when it shows far to much Uf on a cap in circuit that it may be a false reading. But this hasn't happen to much.
Don't go for a cheap cap meter. Get one that is designed for in circuit tests.
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.