My own experience
I concur with Montyb. There are times when I can see patterns and guess the next word from context, or from knowing what the person being quoted usually talks/talked about, and other times when I couldn't see the pattern to save my life. I've been solving cryptograms for over 30 years, and I still get stuck much more often than I'd like. Hang in there and try to pass on fewer and fewer puzzles. There are many people on this site who help when they can if you really can't get one. I will usually stay with a puzzle until I solve it, no matter how long it takes (sometimes 30 - 45 minutes).