Over Grown Lawn.
To restore an over grown lawn you are best to cut it back slowly a stage at a time never reducing the over all height by more than a third of the total length of the grass blades at any one time.On a very long lawn this might involve cutting the lawn with a strimmer and raking the cut grass off the lawn.
So the program should be to cut the lawn by a third 10 days in the spring until its down to less than 25 mm.Then depending on if there are any weeds or not you can cut it every week.
Most of the weeds will die with the cutting as they will not be able to recover leaving you to stop treat or remove by hand the remaining weeds such as daisies that are able to lay flat under the blades of a mover.