To gain waiter/waitress loyalty I like to pay my bill with a credit/debit card and tip in cash. I fill in the "tip/gratuity" line of the credit card receipt as "0" giving them the option to claim the cash or not. It is a small victory for them but much appreciated.
My GF and I are regulars at our favorite haunts and over the years have been given our fair share of comps and more importantly honest information about menu selections
(always interesting to see the eyes dart left and right, the pleading "no not that" look, and the inconspicuous head shake) . Also if we are given free desserts or drinks, I figure in the missing cost and apply the appropriate amount for the tip-this works wonders.