The following information has been provided by Great Ormond Street Hospital.
If you have not ridden a bike in a while, GOSH staff frequently advise hiring a Santander Cycle near a park and having a go on a traffic-free path.
If you are keen to go further, either ask a colleague/ friend to guide you on a safe route, or try a TFL quietway/ cycleway route which has segregated bicycle lanes, or very low traffic routes. https://tfl.gov.uk/modes/cycling/routes-and-maps/cycleways
Transport for London provides a free online cycle skills course comprised of 4 modules: