Why do I get constant punctures?

There can be many reasons for punctures, the most common reasons for repeated punctures are:

Minute debris stuck in the tyre – could be too small to see, but sharp enough to cut the tube - Tyre replacement needed
Pinching of the tube between the tyre and rim – be careful of positioning the tube back in the wheel
Metal burr left from the casting of the rim – cured by flattening the burr gently or rim tape
The end of a spoke being too sharp – cured by flattening the spoke gently or rim tape
Inconsiderate/inappropriate riding style with jumping/bumping against kerbs – rider education
Worn beading on the inside of the tyre – this is where the metal strands which run through the underside of the tyre have worn and come out of the rubber after being deformed - Tyre replacement is needed