Graphite is an effective and inexpensive solution to help lubricate your door lock. It's a dry lubricant and doesn't attract dust like oil based lubricants do. You can find it in many pencils but it is also available in small tubes for lubricating purposes. It's easy to apply and doesn't make a mess. However, it does leave behind a fine powder that can stain hands, pockets, and tables, especially if you do it overly often.

The key to this method is to coat your key with the graphite and then insert it in the lock repeatedly to grind the chunk of graphite into a fine powder. This will lubricate the lock and unjam the tumblers to help it turn. However, it may not be a permanent fix and you will need to repeat the process if you continue to have trouble with your lock.

If you use this method to lubricate your lock, it is recommended that you reapply it every 6 months to ensure proper operation of the lock mechanism and prevent the accumulation of dust. You should also consider using a professional locksmith service if you're having consistent problems with your lock.

If you're interested in a more long-lasting and cleaner solution, there are plenty of other options on the market. Some of these include spray-based graphite lubricants that are specifically labeled as "dry" and don't contain any oily residue. Another popular option is a PTFE lubricant that is made to last a long time and prevents rust, corrosion, and freeze-up in outdoor locations.