Make sure you arrive at London Heathrow airport (LHR) at least 3 hours before the flight if it is an international flight or 2 if it is a domestic one.
Check the luggage limits
(size, weight, items forbidden, etc) with your airline.
Have all the documentation to carry out the check in (flight reservation number or boarding pass, passport, Visa and vaccination documents if apply).
available towards the London Heathrow airport (LHR) and the Terminal where you depart. If you arrive at the airport by car check the airport
Check the Facilities and Lounges
(if available) within the airport grounds, to organize your waiting.
Once inside the terminal, look at the electronic screens to know the status of your flight. If necessary, declare your new electronic devices at the Tax office.
At the check-in desk (if necessary) you can check the big baggage, show your reservation ticket (printed or in your phone) and passport and receive your boarding pass. In case you don't have to check a luggage, some airports have self-service check in kiosks where you can get and print your boarding pass or can do it online since 48 hours before the flight.
Then, at the security control area, if you bring a laptop or a similar device, you will have to place it outside the carry on bag and in a separate basket. After passing the security area you will get in at the boarding zone. Check you boarding gate and wait the airline call, always having in hand your passport and boarding pass.
If you are a handicapped passenger, you should coordinate your trip with your airline at least 48 hours in advance and check the
facilities. Enjoy your flight!