After sowing fresh seed, cut the grass when the stalks reach around eight centimetres. Cut it to around five centimetres now; when the grass is mown for the third or fourth time and is thicker, it can be gradually cut to three centimetres.
There is no benefit in letting the lawn grow really long and then cutting it right back. The stalk always needs to have a certain length to enable photosynthesis, which is why it is better to cut grass little and often rather than all at once. For each cut, the rule of thumb is to shorten the stem by around half to two-thirds to 2.5 to 3 centimetres. Only lawns in less sunny areas can be left slightly longer, until the grass has a stem length of around five centimetres.
There really is an ideal cutting technique. We have partly addressed this issue already through the information about the cutting heigth: Little and often is better than all in one go. Each time you mow, change the mowing direction. Otherwise you will always press the stem in one direction, which results in easier thatching of the grass. If you usually mow grass to the right, alternate with mowing to the left. Occasionally, you should also mow diagonally, changing sides. If you want to produce a strip pattern like that which decorates stadium grass, for example, you need a mower with a roller at the rear. The roller flattens the grass in one direction, making the bright, shiny underside of the grass visible. You can use this technique to create stripes, squares or circles on your lawn.