Just be yourself, relax, have a good attitude, and everything will fall into place. It really is that simple. When customers see your bright attitude, they will automatically trust you, and want to talk to you (ie. have a conversation with you about the food there, how long you've worked there, or anything about you and not necessarily about the restaurant). When they feel connected to you this way, they will naturally want to leave you a 15% or larger tip.
Pass by their table 2-3 times during the meal so that they know you're around in case they need anything. It's not necessary to talk to them or do stuff at the table everytime you pass by because then they'll feel they're not given freedom to take their time and enjoy their food.
When I go to a restaurant, if the waiter seems to enjoy his job (which you always should no matter what job you're at, otherwise you'll get grumpy and snap at customers, and that means NO TIP!), is patient explaining the menu (even if I am tempted to get impatient and just want to read the menu alone, I still can't be mad at him =) ) walks by a couple of times during the meal so I know he's doing his job and I can call on him for anything, but does not interrupt my meal all the time, because this will make me think you just want a big tip, and want me to leave soon. By the end of the meal, I will tell the waiter how grateful I am for the meal and his service. And then I will almost
always leave a 20% tip, and if the meal was small, maybe even a 25% tip.
It is important to remember though, that although everybody wishes for a bigger tip, a tip is still an option, not an obligation. If you think of it as an obligation, customers will feel your pressure, and think you're not genuinely sincere about your service. You'll either end up trying to hard and pushing the customer away or completely ignore the customer. I've had experience in both and neither is pleasant. For the waiter who wasn't around at all while I saw other waiters going in and out frequently, I knew she was lying when she said "something was wrong in the kitchen" and that's why my food was taking a long time. As for the overly pushy waiter, I had an instance where one waiter asked me if I'll like an additional can of soda. I thought, that wasn't a little too much, And is misleading making me possibly think that it is like a free refill when it is not. The same waiter at another time, took my unfinished can of soda and poured it into my glass for me. I was taken aback thinking, that was rude, because while some people might think he's being VERY helpful because he just wants to take away a soda can, I'm thinking I have my reason for not pouring all of the soda from the can into my glass (I didn't want all my soda to get diluted with ice too quickly while I eat).
So the bottom line is, be around, but don't badger the customer. Helpful, and not annoying. Good luck.