The internal workings of the cylinder should be lightly sprayed with a silicone lubricant (or similar) every 4 weeks. A suitable, widely available product is GT85. Dry graphite maintenance powder is a suitable alternative. Do not use WD-40 or oil-based lubricants as these may attract debris.
It’s very easy to do. If you are using GT85, spray it into your Euro profile cylinder whilst inserting your key in and out several times. If the internal side of your cylinder features a thumbturn, this will also need lubricating. Spray the silicone lubricant into the gap in the neck of the thumbturn whilst turning clockwise and anti-clockwise. Doing so will keep your lock operating smoothly. If you are using dry graphite maintenance powder, follow the instructions provided.