Growing grass in the shade depends mostly on what type of shade is involved. If nearby buildings are obstructing sunlight, you may be better off planting shade-loving ground covers or using decorative mulch. If a deciduous tree is casting a shadow, trimming it to allow some dappled sunlight to filter through to your grass will do the trick. Choose shade-specific grass seed mixes to grow in shady areas. In some cases, dethatching may be necessary before sowing grass seeds.
Trim lower crossbranches off deciduous trees that are blocking the sun. Use a pole saw and a ladder to carefully remove these branches. Account for the aesthetics of your tree-trimming.
Dethatch your shady lawn, using a dethatcher or a dethatching rake. Thatch is the accumulated dead or dying debris that naturally gather between the leafy tops of the grass and the soil. Some thatch is good, but more than 3/4 inch may be preventing your grass from getting the nutrition it needs.
Sow shade grass seed on top of the soil, using a spreader set according to package instructions. Make sure that the seed mix you choose says that it is meant for shady areas. Also, choose a mix rather than a single variety of grass. That way, if one type of grass does not do well, chances are another one will.
Apply fertilizer, using a spreader at the rate recommended by the package. Choose a slow-release, non-burning fertilizer for best results. Slow-release fertilizers last a long time before you need to reapply. Check individual packages for reapplication periods.
Rake a thin layer of topsoil or compost over the area where you have seeded the grass. Keep it very thin. This protects seeds from hungry birds, but grass seeds need light to germinate.
Water twice daily, every day, for 10 days while seeds are germinating and establishing themselves. Water for 15 minutes each time. A garden hose with a sprayer attachment set to a gentle shower or mist setting works well so you do not disturb seeds or soil. A sprinkler also does the job, as long as you make sure all your grass is getting watered. Do not overwater. If water is sitting on top of the ground and not being absorbed, you have overwatered.