Improving my Lawn

I have a very small lawn at the back of my house which i planted from seed last March by August it was still very patchy so i turned the soil over again by hand and planted westland grass seed first time it was Canada green which turned out really nice and thick but now it is all patchy again the soil is very thick and has a lot of clay in it i did work some farmyard manure and sharp sand into it i was just wandering if there is any way of improving the thickness of the lawn this year when it grows maybe by putting a layer of compost on the top now so as it sinks down and mixs with the clay. My front lawn is quite the opposite it is very thick all year round. My back faces east with plenty of daylight but because of the soil type it holds the water, I have avoided walking on it all winter but it has not made any difference and i also left the grass 3 inches tall from when i last cut it in October any tips would be most helpfull

 

1)you could abandon grass and go for chamomile lawn
2) try to aerate with a fork as soon as it has dried out a bit, scarify and top dress with more seed of same variety as last time

 

Besides aerating, and raking the thatch - I would suggest feeding it once it starts growing again - and keep it trimmed. Blades set high at the beginning of the season, and then lower. Cutting the grass and feeding should cause it to fill out - unless there is something in the soil that is not good for plants. Clay other than when compacted or water logged is not a problem