1.  A good memory 
2.  A well organized 'keep track' system
3.  Lots of email storage space

Since my memory is horrible; I'm terribly 
disorganized; and my email server can't manage to 
store anything for more than a month; I've never 
felt like I could keep a promise of dibs.  So I 
don't offer it (like I said before) even just to 
make 'polite conversation.'

I must say I've been terribly lucky to have other 
people remember me when they put up cels for sale 
and I asked about them.  I've gotten back one 
beautiful cel of Neptune and Mars with an 
incredible painted forest background essentially 
thanx to dibs.