The flat I live in has condensation in the winter with little puddles of water forming - please can someone advise the best way to install air bricks to help with the condensation ? Thanks

Yes you could put a air brick in but most effective with the hole cut out,Have you thought about installing a condensation extraction fan,This would only kick into action when a certain condensation/humdity builds up in the room only draw back you would have to get a sparky in to do this,Hope this sounds ok

cut out the dimensions of the air brick on the outside wall at the side of the window (top) along the mortar if feasible. from the outside hole pierce a hole through to the inside so you know where the cover plastic vent goes .Inside cut a hole smaller than the plastic vent fix to wall point around air brick outside

Condensation extraction fan will work comes on when humidity is in the air don’t dry washing on radiators also close the door in the bathroom let the fan do the work leaving door open when showing causes more condensation hope this helps