This is a critical time for your bees. As the days are becoming longer the queen will starting to lay more eggs and the colony will use more of its supplies of food for the brood. It is often at this time of year that they can die from starvation - due to inadequate stores of honey from the autumn.
If the weather is good and the bees are flying, you can have a quick look inside the hive. You should not disturb the bees much. If you find the stored are very low - then you need to emergency feed. You can also gain any insight in the state of colony by watching the entrance of the hive. Bees should be coming and going with pollen for the brood.
April Flowers and nectar should start appearing. The brood will expand and it is a good to time to find and mark the queen. If you wait till later in the year, it is sometimes hard to find her. You should also do a spring clean of the hive, replacing any frames which are not in good condition and removing any brace comb.
May The brood will be expanding at its faster rate and hopefully the weather will be good. You will need to start inspecting the colony regularly and watching for signs of swarming. You may also need to add a super and a queen excluder.