Heads
Heads that are fairly to brand-new and, which have no dents or scratches are essential. if the head is not completely even, it cannot be in tune and ring true. Even if a head is old but undented it may not work  - it has probably stretched, and will be of uneven thickness.

Preparation
Remove the old heads. Clean  the hoop and bearing edges, removing dust, stick debris, and any build-up (beer?) that is found. Now is also a good time to do any drum cleaning or polishing, as there are no tension rods or hoops in the way. Do not use any liquid (your drums are wood, remember?

Fit New heads
Place the head onto the drum and spin it around the bearing edge to ensure clean contact. Tighten the tension rods until they make contact with the hoop. Do not tune yet.

Tuning
Put the drum flat on the floor. This deadens the head at the bottom of the drum, allowing you to isolate the head you are tuning.

Following the order in the diagram below, begin tensioning by turning each key rod 1 complete turn, then continue using a quarter turn at a  time, until the lowest possible pitch the head will resonate a is reached. Tap around the circumference of the head listening for high and low spots and correct accordingly. 

Flip the drum around and tune the bottom head to approximately the same pitch as the top (batter) head. The overall sound of the drum begins by setting the pitch of the batter head and then getting the bottom head close to that pitch.

Note: If you tune both heads to exactly the same pitch, the drum will be large and "boom", filling more space in the mix (good for slower or more uncomplicated music). If you tune one head slightly sharp or flat of the other, the sound will be tighter (more controlled).

Whether the Final note you go for is low or high tension is a matter of what you like, but the drum should be able to support the note without "choking" (when the head is too low or too high, the notes cut off quickly, i.e. no sustain).