Once a year, either in spring or in autumn, both, if I am really motivated, I dethatch (vigorously rake out any dead grass that has built up) and core (give the area a good fork over to loosen the soil). Coring reduces compaction and improves aeration and drainage.
In autumn, I feed the lawn with MAP (fertiliser also know as monoammonium phosphate), hoping that the phosphorous it contains will improve root growth. I never bother to measure amounts out and just randomly broadcast it over the area.
Then in the spring, as soon as the weather warms up I spray out the winter weeds with MCPA (herbicide). MCPA does not affect annual clover, which I like to leave for its nitrogen fixing properties. Then, I fertilise with urea to kick start the growth for the warmer months. Since I use inorganic fertiliser, I also give the lawn lime every couple of years, to regulate the pH. Also, when applying lime and/or fertilisers do not forget to water before and after.
I am by no means an expert and my tips should be taken with care.I would like at least two more seasons before I am willing to say how well it works, just in case it was a lucky season or something.
I think that is it, if I find myself doing something that was not mentioned, I will update you.
I hope this was helpful. :)