Kneeling at the side of the bike, grab the cranks. Rock the crank side to side to see if there is any play in the bearings. Hold the pedals and try to do the same. You should not feel any play in the bearings. Select a gear on the front and rear gears that gives a straight chain line from the front chainrings to the rear sprockets, then rotate the cranks backwards. The cranks should rotate freely and the chain should not skip and catch on the sprockets. Also check that the sprockets for any missing teeth and that they are not twisted or bent.
Drivetrain – Gears
Check that the front derailleur runs parallel to the chain rings and that it cannot be moved under load. Make sure that the cage of the rear derailleur sits parallel with the rear cassette and it is therefore not bent or out of alignment. Most drivetrain issues are a relatively straightforward fix for the home mechanic, here is a blog on adjusting a rear derailleur gear.
Keep your frame in clean condition and give it a good check over now and again. Inspect the head tube, top tube, down tube, seat tube, chain stays, seat stays, and around the bottom bracket. Listen up while riding too – any odd creaking noises? Check for any dents, cracks or ripples in the paint work of your frame. Any issues found on the frame are a major safety issue and therefore the bike should not be ridden, if in doubt get it professionally checked. Here’s a blog on investigating Bike Noises.
Saddle and post
Holding the bike by the saddle, try to twist the saddle to ensure the seat clamp is properly tightened. Apply vertical pressure to make sure that the bolts holding the saddle to the post are secure and tight. You should not feel any looseness.