The only real suggestion I have is to put together some 'what if' scenarios for intercepts; for example, I'll usually consider...
What if target maintains course, and moves at 6kts for the next X hours? I'll estimate that distance and potential position with the ruler. What if they move at 9 or 12kts instead? This gives you a pretty good search range to cover, and lets you make a few risky gambles. If it's a small convoy, you don't have too much of a lost opportunity if they slip by you, so I may try and head them off supposing they're moving 9kts. The risk being that they could blow right by me if they're moving quicker, but like I said, if it's a low-priority target, you've lost nothing but a bit of time.
Other things to consider are logical course changes. If they're moving near a coast, and there happens to be an enemy-controlled port further along the coast, there's a chance they might just be following the coastline.
When all's said and done, it's an art, not a science; the only thing that'll really help you is practice and experience.
