Like virtually any other relationship-oriented activity in the workplace, the Backscratch is a game with rules that no one will actually tell you, but you are expected to know nonetheless. S'ok. I'll tell you.
The most important rule is that you never say the following three words: "You Owe Me." If you say those words: YOU LOSE.
The Backscratchee knows he owes you one. To actually come out and say he does is to remind him that at some point, he needed your help--when in retrospect, he will usually think that he could have done it without your assistance. Besides, saying You Owe Me is bad form.
Eyeball the situation. Step back and assess whether the coworker might interpret your offer as presumptuous or patronizing: "Let Mamma help you pookie poots, cause you couldn't possibly solve this big nasty problem by your own silly little self." If you so much as think it could go that way, skip it entirely.
Favors are offers, NOT advice. Do not say anything that starts with the words "I Just Think You Should... or "You Must..." Those phrases mean you aren't a helpful, loyal, sympathetic party, but an obnoxious buttinski or potential backstabber trying to make your coworker look bad. Always say: "Is there anything I can do to help?" That way, the coworker actually asks you for help, and is less likely to feel threatened by your ability to provide it.
Don't let anyone pressure you into doing something you don't want, or feel equipped, to do. If you DO agree to do something you would rather not do, remember, it was your choice. Breathe not one word of complaint.
No Martyrdom. If you do someone a favor, don't keep reminding the coworker about it while you are doing it: "You are gonna owe me Big Time for this one!" No bitching, no guilting.
Statute of Limitations. You can't give a Backscratch 42 years ago, never collect on it, never keep in touch and then waltz through the door asking for the favor of his next dance. You must renew contact at least once a year--at the very least, send an annual holiday card.
Never demand payment. Ask the coworker for the favor you want, and make no mention of the previous assistance you gave her. If she can't deliver the requested favor, be gracious and let it go; she'll still owe you one. If she outright refuses, then you know the score with her--she's a User Jerk. In that case, be tactfully unavailable to her for future help, unless, of course, she's your boss.
When someone helps you out above and beyond the call of duty, make sure you appropriately acknowledge the favor. Lola was trying to help out young Stacy, who said she was trying to start up a business. Lola gave Stacy tons of time, advice and equipment among other favors. Stacy said "thanks" when she picked up the computer, but never stopped to follow up with even so much as a "thanks again" email. The next time Stacy contacted Lola, it was to ask for yet another favor. This time Stacy was ever so unavailable to help. Honey, don't ask for another favor from the same person, if you never appropriately acknowledged the first. Hint: Think hand-written note or small giftie.
I once helped Lisa out with her business plan and as a thank you, Lisa sent a gift certificate for a massage. I did not expect anything in return for her assistance, but was so surprised and touched by the gesture, she has never forgotten Lisa's thoughtfulness. That was years ago, but to this day, I feels very loyal to Lisa and will always give Lisa a hand with anything she needs. That's how it works.
Email me with any good backscratch stories...