Once the tenant has given notice he will be leaving, you can start showing the place.
Please note you don't require written notice if the tenant consents to entry. With 99% of our tenants, we text or email them to ask permission for entry. This way they feel consulted as to a convenient time, and we don't have to pay our runner to deliver notices. We only deliver notices to tenants when we suspect trouble may be brewing.
Oh man, I love tenant turnovers. They are so much fun. This is the part where you will really get to benefit from having a relationship with the tenant prior to move out. Great advice provided above.
In agreement with Sherilynn, do a thorough walk-through of the property (with pictures) and put together a package that outlines any damages that require repair. Many small fixes can be accomplished by the tenant at minimal cost. Having that relationship in place will make the 24 hour notice much less important as it is likely they have damaged something and if you come to an agreement to keep the place neat and tidy then you will overlook the damage.
Showing the place more than 60 days out is probably a waste of your time anyway. I don't bother until ~40 days before.
As a part of improving your landlording systems, you should also provide the new tenant with the move out checklist. Both tenants receive information on how to forward their mail, cancel utilities, ect.
Communicate in person as much as possible! Provide written confirmation afterwards. Many tenants ignore their mail so make sure they understand their responsibilities before it is an issue.