For tolerable urges - do something I really enjoy doing (for me: playing games, watching a DVD. dancing around my room).
For bad urges - I write down my feelings in detail, in therapy I learnt that I have a tendency to go 'I feel really bad' but never identify why. Nowadays I make a list (mental or physical) of what is bothering me then either find solutions or realise that I'm upset about nothing. Crying. The elastic band thing as the last resort. Staying away from the rooms that I used to harm in. Calling my best friend.
For urges in a public place (the pub etc): Wearing a hair bobble on my wrist just in case, relaxation techniques, calling my best friend (again!).
For general reasons to stay self-harm free: proving everyone wrong; staying happy; not having the stress of buying tools or covering up; no new scars; (eventually) short sleeves, going swimming, going on holiday; not upsetting my family and friends; being in control of my life; the prospect of becoming a teacher; the future in general; knowing that I overcame something difficult.