If you find it difficult to insert your key into your lock a light puff of graphite power will often help.
As it is dry based it will not attract dirt or dust which is the complete opposite for oil based lubricants.
Never spray wd40 ect or any oil based lubricant in to the lock cylinder as when they mix with dirt or dust will turn to a thick mixture ,,the tolerances in a lock cylinder are very fine and it doesnt take much to diminish the gap causing friction to occur.
Also be aware only apply a light puff of graphite powder is required , and then insert your key in and out several times to distribute the graphite powder.
Pay attention to the key for signs of the black graphite power which will indicate that you have enough inside the lock cylinder.
Too much graphite will stop your key from entering fully ,so be aware excess amount will cause a problem.
If you find you have puffed to much powder do not force the key as the powder will compact at the rear of the cylinder.
Place a straw and blow excess out while wearing eye protection.
You can also insert some fine wire and remove excess powder
Fell free to contact Arrow Locksmiths if you have any question about the procedure