As spring approaches and the temperature begins to warm up (50 degrees or warmer), the hive becomes more alive with action. If you see activity on those warm days, it is a good sign. If it looks like they are alive and the honey is gone, sugar could be put on the top board. Look for the queen or capped brood.
If you have a strong hive consider putting a sheet of newspaper and a honey super on your hive. This will keep the hive warm but will give the bees room to expand, if needed. They will eat through the paper. If you are concerned about swarming, consider using the Demaree method
(http://countryrubes.com/images/Swarm_Prevention_By_Demaree_Method.pdf ). If you think swarming is inevitable and queen cells are present, pull some frames with queen cells and put them in a nuke with some empty frames.
Mites - In the spring, the mite count is generally low. However, if you want to treat for mites, Formic Acid can be used during honey flow and when supers are on the hive. Drone cells promote mites. HopGuard ( http://www.betatechopproducts.com/products/varroa-mite-control ) can be used when installing your new bees to control Varroa Mites. Apiguard ( http://bees.tennessee.edu/ipm/apiguard.htm ) is another treatment for Varroa mites.
Small Hive Beetle - Formic Acid can be used to help repell small hive beetle ( http://www.mitegone.com/pdfpages/Small%20Hive%20Beetle.pdf ).
Nosema - Nosema apis is a winter time parasite that causes diarrhea and in the spring and summer the bees can get rid of it. Nosema ceranae stays with the bees year around. It does not cause diarrhea and is more difficult to diagnose. Fumagillin-B can be used in the spring to treat for Nosema. It must be treated before honey supers.
American Foulbrood - Medicate with either tylan and terramycin. Then the treat with the other in the fall. Must be treated 22 days before honey supers are put on the hive. It is important to follow the directions precisely.