The Law
On public highways, cyclist must follow The Highway Code. In particular, make sure you know the additional rules for cyclists.  You do not have to use a bell but you must have lights front and back at night.  It is illegal to cycle on the footway (the pavement next to the carriageway) unless it has been designated a cycle way but it is not compulsory to use cycle routes.

Bike condition
Check that your bike is road-worthy before setting off. Here are a couple of nice simple check lists: one from the Richmond Cyclist Training Scheme and the other from GOOD. Remember that bicycles must have working front and rear lights to ride at night.

Cycle skills

You are safer if you have good bike handling skills and know how to negotiate obstacles and traffic. If you want to brush up your skills and/or develop more confidence you can always book a session with an accredited cycle trainer.

On the road it  is important to both see and be seen - occupy the centre of your lane or ride at least half a metre out from the kerb.  You can always move closer to the kerb if somebody overtakes too close, but if you are already in the gutter you have nowhere to go.  Indicate to other road users what you intend by road positioning and by looking, signalling and then moving when safe to do so.  At junctions occupy the centre of the lane whether you are turning left or right.  Be alert and anticipate the actions of others and if possible make eye contact.

Keep calm and avoid getting angry or having arguments with other road users when they misbehave.

For more advice go  to  British Cycling  or   cycletraining uk

British law does not require you to wear a helmet although the organisers of some cycle events do require helmets to be worn. Helmets do not prevent accidents and there is conflicting evidence on their effectiveness in the event of a crash on to your head.   The actual risk of head injury is remote, less than crossing the street, walking up stairs, climbing a stepladder, skating, travelling in a car, etc.   Wearing a helmet is therefore a personal decision.

A head injury can occur if you come off head first over the handlebars if you brake suddenly using your front brakes only or if riding down a steep or bumpy section on a mountain bike and not keeping your weight over the back wheel. Learn to brake safely!

Helmets must be fitted correctly or they can cause injury or obscure your vision.   

Hampshire Constabulary provide tips to keep your bicycle safe. Includes advice on recording your bike description, registering your bike and locking your bike.