Don't wait until the airport to check-in if there a "limited" number of seats already, you'll be stuck in the middle somewhere with a stranger sat beside you!!!

Best to take the advice offered, OLCI, grab the seat you want, complete the checkin process but don't print your boarding pass. You can then use a self service machine on the day of the flight and see if there are better seats, wait at a check in desk and talk to one of my ground colleagues, or keep checking daily and grab yourself anything that appears and takes your fancy...

As long as you never print your boarding card or send it to a mobile phone during OLCI your seat will be yours but won't be locked so you can still change later.