The first thing that you need to do in order to clear a building with a firearm is to choose an appropriate gun. The weapon of your choice will depend heavily on the type of building that you will be attempting to clear. You may find yourself having to choose between a gun such as a handgun or automatic, or a grenade. You will also have to consider the number of targets that you may encounter while selecting the weapon. If you are likely to run into multiple targets, you will need a weapon that can fire quickly and handle multiple rounds. In situations like these, handgun and shot-gun will not be the most appropriate choice. Automatic weapon and grenades will be a good option.
Once you have selected the most appropriate weapon after taking the building and number of possible targets into consideration, you need to formulate a plan, or course of action to be more accurate. This would require you to take the design of the building and its entrances into account. You will again taking the possible number of targets you may encounter inside the building into account while choosing a course of action in order to deal with them in the most effective manner and without sustaining any damage.
Once you have come up with the plan and taken all factors into consideration, prepare yourself to put the plan into action. Remember to move as covertly as possible, so as to avoid alarming the targets of your entrance and movement. When you reach the corners or the doorways, execute the right technique to get across them or enter them. Remember to be cautious and on your toes at all times, especially when you reach an area where you have no choice but to put yourself in a vulnerable position.
Locate your targets and neutralise them. You can either immobilise your target by knocking them unconscious and waiting for the local authorities to handle the situation from there, or shooting the targets with the intent to kill.