Measure people against their own performance, not other people's. Avoid contests which reward only one or two people. Create team or buddy contests or have people work for percentage improvement. Don't trust what people say about reinforcement. Many say they just want money.
Appreciation is an important motivator, but people are often unable to ask for it.
Noticing improvement and immediate reinforcement is primary. Keep bravo cards, applause notes, or other items on hand that make reinforcing on the spot easier. Design a point system to give daily or weekly points as an immediate reinforcement for a longer term payoff. For example, weekly goals can be scored by percent accomplished. A goal of 300 points can usually be earned in four weeks using this formula.