There must be some wear indicating lines on your brake pads. If you don't see them - it's time to replace the pads.

You can measure the stretch of a chain with a chain gauge (or just a ruler)
Alternately - the chain links are 1 inch long, so measure 12 of them with a ruler, if they are more than 1/8 inch longer than this then they are worn.
You need to do this before it wears the rear cogs - it will cause the teeth to wear into sharp pointed spikes = need a new cassette.

The psi required will be stamped on the side of the tire
Measure the pressure with a tire pressure gauge

Do a full tune up every 3-6 months depending on how much you ride