Free drink if you show the cashier an honest and positive Yelp review you just posted about your meal!
First of all, welcome to the site!
Unfortunately (or fortunately, depending on your point of view), Yelp specifically prohibits paying for good reviews. However, having discussed it with a Yelp rep, it IS OK to encourage customers to write reviews, as long as the ones who write bad reviews receive the same treatment as the ones who write good ones ("free drink if you show the cashier a Yelp review you just wrote"). Although it is true that very few people would show a bad review and ask for a free drink. Also fine with Yelp rules is a sign that says, "If you enjoyed your meal, tell Yelp. If you didn't, tell US!"
A problem I have in writing Yelp reviews is whether to rate a place on an absolute or relative basis. A hot dog stand may be the best hot dog stand I've ever been to, but it's still a hot dog stand. I tend to review on a relative basis, and would give it 5 stars. My own point of view:
1 star: Stay away!
2 stars: I'll go there if I have no other option.
3 stars: I will go there, but if it disappeared tomorrow, I wouldn't miss it.
4 stars: Really good, but there is room for improvement.
5 stars: One of my favorites.