There's two basic problems you have to deal with when cooking poultry.
1) Too much heat for too long can cause poultry proteins to denature and squeeze out natural juices, which results in a dry and chalky texture and significant reductions in flavor. This problem has been exacerbated by modern poultry production which produces a leaner product that's more susceptible to overcooking.
2) Consuming poultry products has an inherent increased risk of salmonellosis, which at worst can cause death, but more commonly results in less major gastrointestinal illnesses.
The challenge is that undercooking to correct for #1 can result #2 (in more ways than one, pardon the pun), and overcooking to correct for #2 can result in #1.
Dark meat like turkey legs are easier to cook because they have a higher fat content and are less forgiving of overcooking, but not everyone likes dark meat.
There's at least two strategies you can employ to correct for both problems, either independently or preferably simultaneously.
The first is the application of salt to the interior of the meat. Salt not only adds flavor, but causes the proteins to retain moisture. Many people like to accomplish this by wet brining in a 5-10% brine solution (5-10% salt to water ratio, by weight). If I have the time, I prefer to liberally sprinkle salt to the outside of the meat, and cover loosely with plastic wrap and refrigerate for about 24 hours. This is the dry brining method and both are described in the link.
The next strategy is temperature control. There is a band of temperature and time that results in a safe result, without overcooking. This method is the essence of pasteurization and relies on both time and temperature throughout the interior of the meat. For home cooking, the government recommends cooking poultry to an internal temperature of 165F. The problem is that's about the temperature at which poultry starts to become dry and chalky, and if you leave it in the oven till that temp is achieved, you can easily overshoot that mark with residual cooking that results after you remove it from the oven. It's entirely possible to render poultry perfectly safe at temperatures as low as 136F, but you must be able to hold that temperature for longer periods of time. A method for cooking to lower temps is described in the link, which is for chicken breast, but can be adapted for turkey. It does require a good meat thermometer, and there's lots of different products which will do this in the range of $20 to whatever you want to pay.
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