Ideally the weather will be still and warm, avoid opening the hive if it is raining. There will be fewer bees in the hive if you open it during the day when all the flying bees will be out foraging. When you take the roof off, place it to one side, don't put it in front of the hive entrance, as anything in the path of returning bees will annoy them.
Not every colony reacts the same to being inspected. Some are very docile and will hardly need smoking at all, some will benefit from being smoked at the entrance and then by lifting one corner under the cover board a few minutes before the hive is fully opened. This allows the bees to smell the smoke and they will have time to eat some honey, which makes them easier to work with.
Looking Out For The Queen
Once the cover board is removed, check it to make sure that the queen is not on it. It's unlikely, but if she is then it's important to return her to the hive. The best way to do this is to walk her back into the hive by guiding her in with your finger. Alternatively let her walk up onto your hive tool by placing it in her path. Once on the tool return her, ideally to a brood frame. Most likely she will quickly scuttle between the frames. Take great care doing this as any damage to the queen's legs can severely impair her ability to lay eggs.
At this point you may need to apply a little smoke to the top of the frames as bees make their way back up to see what's happening. You may notice some standing on their hind legs swivelling around following your movements. These are the guards but a little whiff of smoke will send them back down again leaving you free to carry on.