Before a ride
Plan the ride using a map, noting emergency escape routes. Tell someone (a spouse, friend, relative) where you are going and when you plan on returning (remember to also call them after you have returned!)
During a ride
Don’t drag your bike through streams, throw it down steep slopes ahead of you, or subject it to forces it wasn’t designed for (dirt jumping a cross country race bike, for instance). Learn how to ride lightly on the bike and use the brakes as little as possible. Take the pressure off the pedals when you change gears.
After a ride
Clean your bike after every ride. Some people prefer hosing it down, others prefer a bucket of soapy water, others still prefer to let the crud dry on and then brush it off. Never, ever, pressure wash a bike or even spray water at bearings and seals as this forces dirt and water into the moving parts. “Sealed” bearings aren’t watertight.
After cleaning the muck off, wipe the bike down with a clean dry rag, and then optionally clean it up with spray polish. Applying this tender loving care lets you inspect the frame and components for cracks, dents, chips, corrosion and other signs of impending doom.
After washing the bike off, re-oil the chain. Wipe off any excess lube as soon as you have oiled. The chain should look dry – the only useful oil is inside the moving parts, not on the outside where it can pick up dirt which wears away the chain rings and cassette. Don’t use WD40 on your bike because it leaves a sticky coating (although you can now get WD40 brand wet chain lube and dry chain lube, which are OK to use).
Fix all the things that were annoying you during the ride – the shifting that was slightly off, or the wobble in the front wheel. It’s always nicer to work on a clean bike, and this way you may find the beginning of a major repair – bent chain or worn rims – while you are at home rather than suffering the consequences on the trail.
Store the bike right-side-up or hanging by its front wheel from a wall. Hydraulic brakes tend to dislike being upside down even for short periods of time as air bubbles congregate in the caliper. Fork oil also tends to appreciate being the right way up so that it remains on the correct side of the damping valves.
Restock the supplies in your trailside tool kit – make a list of what you need to buy, and make sure you get to it.
Do it yourself or pay someone to do it. Remove and clean or replace the chain. Check the brake pads. Check tire wear and replace if necessary. Adjust or replace shifting and braking components.
Tip: Treat yourself to some new handlebar grips, cables and cable housing. This is the cheapest way to make your bike feel like new again.