The choice between laying seed or sod to start a lawn is an eternal one. Both methods have benefits and drawbacks. Seed is less expensive but more temperamental. Sod is pricey, but easy to establish. But whichever method you choose to start your lawn, the key to success is making sure that the seed or sod has good contact with the soil. Some simply walk over their seed or sod to accomplish this job. But a much better tool for the job is a lawn roller.
Fill your lawn roller with water according to the manufacturer's instructions. This can usually be accomplished by unscrewing a cap located somewhere on the lawn roller's drum.
Roll the lawn roller over the planting area after you have prepared the soil but before you lay the seed or the sod. Start at one corner of the lawn and make parallel passes from one end to the other as you would with a lawn mower. The lawn roller will even out the ground to give you a level lawn.
Roll the lawn roller (using the same method you used in Step 2) over newly lain sod to make sure its roots have sufficient contact with the soil.
Roll the empty lawn roller over your newly-seeded lawn to make sure that the grass has sufficient contact with the dirt.