In the home
For doors you could fit a letter box flap or brush and a keyhole cover. However remember not to block up any intentional ventilation such as extractor fans, airbricks, wall vents or trickle vents in windows, as some vents are needed to allow some fresh air to flow in and around your home to prevent mould and damp.
Switch your energy supplier
Be an Eco Home
For inspiration why not look at the Green Open Home Network.
Community Energy Coops
Once you have taken all the measure you can to reduce your energy footprint you can calculate your remaining emissions. WWF has a good calculator or Bulb have a really good calculator and integrated offset scheme. Alternatively you could try the new CoGo App which analyses your bank transactions using Open Banking Data and has a carbon footprint tracker developed with in partnership with climate expert Mike Berners Lee.