Check queen presence and egg laying
When you are searching for the queen, work with care and keep in mind that some of the queens can hide outstandingly well. If you only want to check that the queen is doing fine, then it is good enough to check the brood area. If the brood area is solid, meaning that there are hardly any empty cells within the brood area and there is enough brood in comparison to the number of adult worker bees in the hive, then everything is in order with the queen.
If you need to find the queen for marking, for instance, unmarked queens can easily be found early in the season when there are quite few workers and only one or two boxes in the hive. The queen usually goes to the empty built frames that have recently been put in the hive. You also have to remember that the queen might leave the hive, while the hive is being searched.