Posted: 20/04/2016 at 17:12
I think I should write a crib sheet for this question as you're right it's constantly a question on here. You may well have either clay soil or compaction. Neither is quick to sort out. I'd lift the grass and have a look, try and get a fork into the soil. You'll find it hard to get very far if it's compacted and clay be will wet and claggy. If it's compaction you need to lift the turf and break up the soil underneath, removing builders rubbish as you go. Then you can add well rotted manure and think about laying the turf or seed it. If it's clay dig a hole, a spades depth and see if water collects and how long it takes to drain. The longer it takes the worse the problem. If it's clay there's little long term solution other than to take everything off and dig it adding maure and as much grit as you can which will slowly improve the drainage. If you have seriously poor drainage the best option is land drains.
Sorry I can't provide an easy answer.