You can always lookup your flight on one of the seat rating sites ahead of time (try SeatGuru for example). You'll get a map of which seats to avoid, and data on the seat width and pitch for each airliner. You shouldn't have to "not know" what you're getting for your money if you just do 5 minutes of research.
SeatGuru cant tell me whether a gaggle of 6 yr olds will be placed around me.
You can only pick up so much from seat plans and online reviews. Years of flying experience has taught me a few things (I.E. avoid bulkhead seats, that's where kids go) but even that isn't perfect and I still get horror flights.
The biggest tip I can offer for non-frequent fliers is not to be a cunt. Everyone is in the same situation, so if the person behind asks nicely for you not to recline maybe it would be a good thing if you didn't. If you feel civil enough, you might even be able to negotiate with the person behind you and meet half way. I'm continually surprised by people who go into full retard mode the minute they get near an aeroplane and start "enforcing their rights" whatever they think they are, on everyone else.
The last thing you want to do on an aircraft is piss off the person behind you because it brings out the worst passive aggressive behaviour (and a lot of ordinarily rational people will go into "I lose, you lose" mode when pushed) and they've got the entire flight to make your life miserable.