Dont usually use the exchanges but had a dabble last night and built a nice bank from the "any other score" market in the Lyon game at 22/1.

Anyway, any reccomendations about maybe just making a fiver here and there from backing/laying etc on footy markets? Not arsed if I lose it but would quite like to keep it slowly ticking up on very short odds etc

Depends how much spare time you have on your hands, and whether you are prepared to sit and watch the odds fluctuate to be honest. Even then, the footy markets aren't the best for doing that.

Horse racing is probably your easiest bet if you know anything about it. Can quite easily (when I say easily, it could take a long time) have a bet on a horse where you back it at a price and lay it off at slightly shorter odds giving you a free shot on the horse winning, even if it is only for a fiver. Obviously not guaranteed to win, though.

Prefer footy and would only do it if had time to sit and watch odds etc. Was thinking of just backing say under 3.5 goals in games id expect to be tight and laying off after say 10 mins if no goal for a couple of quid? Obviously would need an exit strategy if an early goal like.

Then yes the over/under market is probably your best bet. I've never sat and watched the odds for it though, don't know how much support this market gets from backers/layers, which is important on Betfair. I'd imagine prem games or TV games you would be fine, and like you say providing there is no early goal you should make your money.

Alternatively, backing 0-0 may be an option as I imagine this market will drop quicker, but again screwed if an early goal, but your outlay won't as much as if you were backing odds-on under 3.5 goals.

Probably just worth watching the market once and seeing how quickly it drops.

If you only want to make small but guaranteed amounts you should try Matched Betting. You will need to have accounts with a few bookies, and then after using the sign up offers you then use the free bet offers. Ladbrokes have a weekly offer, that has to be done on a mobile, where you place £20 in-play on 1 game to receive a free £10 free in-play bet on a game the next day. Done correctly you can make between £6 to £8 per free bet. This weeks matches are the Borer to get a free bet for the Spurs match. Been doing this for about a year, I don't use every offer that is available, and have still made over £1500.
Take a look at this site for info:-https://www.bankofbets.com/ and check out the "Reload Offers" in the Forum to see how many offers are available.