We used to recommend getting arrested and letting the professionals do it for you, but this method is probably simpler.
Things you'll need:
Graphite stick available from craft shops (or a pencil) - Sellotape - white paper, preferably glossy white photography paper. Oh! and a finger!
Rub the graphite stick or pencil on a piece of paper to form a block about 25mm - 35mm square - or round, it doesn't matter.
Rub your finger into the area of graphite, coating it well and enough to cover the area of your finger that you want the print from. (It's messy but it works! :-)
Roll your finger over the sticky side of the tape to absorb the graphite. You may get 2 or 3 rolls out of it from one application of graphite on your finger.
Stick the sellotape down well onto your glossy white paper taking care not to get any air bubbles trapped between the tape and the paper.
Repeat until you're happy that you have a good quality print that can be scanned and still retains the best detail.
If the print is smudged, it's no good. You can avoid this by not pressing down as hard on to the Sellotape with your graphited finger.
Q? Do I need to send the original print to you or can I scan and email to you?
A: Scanning and emailing is fine to do.
Q? Do you recommend 'Inkless Fingerprint Kits;?
A: We've tried various methods for obtaining fingerprints and some Inkless fingerprint kits are quite good and have the added advantage of being a lot cleaner. The charcoal method above is cheap, gives very good results and can be done using items from around (most) homes.
Q? If I scratch my nose with a charcoal coated finger, is there a chance nobody will tell me I have a smudge on my face and end up looking silly all day?
A: Yes, without a shadow of a doubt! :-)