If you don't enjoy paying extra to select a seat on your Ryanair flight, and you have some time available ... you can use the allocation order that Low Cost Routes blog has worked out, to select a seat that you want.
It's worth reading the whole page - but the crucial point is that rows get allocated in the order:
33, 20, 19, 22, 15, 24, 12, 26, 10, 28, 8, 30, 18, 21, 14, 23, 11, 25, 9, 27, 29, 7, 6, 5, 4, 3, 2, 1 (or 1,2, not sure), 17, 16, 31, 32
You can even watch a video showing how one flight got allocated, as an example.
I've used this order many times to avoid seats that I didn't want - it does take up quite a bit of time, as you have to keep checking the Ryanair website. Sometimes you miss out on the seat that you actually want - but I've always managed to avoid a nasty middle seat.
You can also use it just before online checkin closes to work out if a neighbouring row is likely to be empty !