You should clean your kit after every diving day. Your dive suit should be rinsed with clean freshwater, ensuring salt crystals and dirt are washed off. If you have metal zip, zip maintenance using zip-lube or bees-wax is recommended (check your kit manufacturers guidelines what they recommend). Once or twice a year, depending on the amount of dives (or if it smells), we recommend you wash your suit with a mild detergent (there are some special shampoos available for kit). Hang up your suit in an area where there is plenty of fresh air and no direct sunlight. Using specialist hangers are very helpful for this.
Some hints for dry suit owners: There are some silicon pouches you can buy that you drop inside your dry suit to collect any moisture. However, a simple trick is to crunch up newspaper and stuff them down the trouser legs and then replace them every 12 hours until the suit is dry. Your under-suit should never be washed with fabric conditioner - it impacts it performance significantly.
Firstly, inflate your BCD fully and hold it upside down. You will notice water collects inside the BCD regularly. It is quite easy to unscrew one of the valves (careful there is a large O-Ring, don't loose it), use it to pour freshwater in it - swish it around to wash out any any salt water. Take extra time to wash out your BCD inflator, it has a small spring inside which can get covered in salt crystals quite easily. If the BCD smells, you can squirt a bit of Buddy Clean into the BCD, rinse it well to ensure it is washed out fully. Squeeze out as much water as you can, apply a bit of silicone grease (check it is for diving kit) on the O-ring and put on the valve again. Then rinse the BCD from the outside. Afterwards inflate fully (ensure you have undone the straps) and hang it up on a hanger if you can, ideally not in direct sunlight. Check that all your clips for any damage and replace them if necessary.
You should rinse out your regulator 2nd stage while it is still under pressure using freshwater. If not you can rinse it out, but you must ensure that no water travels up the hoses into the first stage or water gets into the first stage. Trapped water will clog up the 1st stage (often giving you knocking noises the next time you use it) - which means an immediate professional service is needed. Let them dry on a towel or similar, or if you have a hook somewhere, hang them up from the 1st stage. Check your hoses for kinks and cracks - especially at the end where the hoses are often surrounded by metal. Replace before they burst. Check your O-Ring (DIN) and replace if shows any sign of damage.
Other bits (fins, mask, SMB, torches)
All other bits should be rinsed with freshwater and can dry naturally. It is advisable to avoid direct sunlight. Check all smaller bits for any damages, mask straps, mask seals, fin straps, etc. Our experience shows, checking them before you put them away in your garage after a days diving is better than trying to fix it when you are assembling all your gear.