Make sure your mower blade is sharp to begin a new season. What type of mower do you have? Electric hover with/without grass box? Petrol driven rotary, with/without grass box? etc.
When you do the first cut of the season you should only remove the top third of growth, (e.g. if it's 3" tall you cut the top inch off), the next cut you take another third off, (2" cut to about 1 1/4" to 1 1/2"). After this, if you cut it regularly, (weekly), then you can fit your mulcher plate instead of the grass box. The clippings are left on the lawn to mulch down and feed the soil.
It takes a bit of time, (and patience), to get your lawn back to a healthy glow after winter. Just don't try any 'miracle' cures and expect to see results in 24-48 hours. A dosing of 'Cut & Feed' or something similar won't do any harm if you want to add something, but don't go mad with a range of different products.