If your driveway has existed for a lengthy period of time, prior to sealing, you must ensure that all stains are removed and/or any existing sealer is compatible with the sealer you are now going to use.
Presently Wolters stock xylene based sealers which are very adaptable in most situations. However care must be taken to fully understand the surface you are resurfacing.
It is usually advisable to wait until the concrete has cured and it also advisable to acid wash the surface area prior to sealing.
Sealer is applied usually in two coats. The first coat sealer is thinned with solvent, usually a ratio of 2 part sealer to 1 part solvent, whilst the second coat is recommended to put on as sealer only.