I use a plastic laundry pail filled with hot water and put the solution
container in that.  I check temperature regularly and shake the solution
container to equalize the temperature within the container and promote
faster transmission of the heat.

Francis A. Miniter

There are probably many methods to control the temperature of
photo-chemicals. One popular device is the Jobo TBE-2 which holds up to
twelve 1 litre size Jobo bottles. This is a very reliable if expensive
option.

I just drop a small block of radium in there.

But seriously, I process film in a Jobo that heats. In summertime, I stick
one of those permanent ice thingies in the Jobo water jacket until it is
just below the temperature I need. I monitor the developer temperature and
when it is right and then remove the artificial ice. The thermal mass of the
water jacket is enough for the entire process.

The water wash is from my regulator valve which cannot go below the cold
water temperature, so for that I hope for the best on very hot days.

For B&W printing, the processing sink contains the overflow from the washing
sink and the washer, so paper processing is whatever I can get out of the
regulator. 75F autumn, winter, and spring. In hot summers it goes above that.

More than one way, I use whatever is easiest:

1) I have a couple of jugs of water sitting next to the stock
  solutions so everything is at room temperature, water from
  the jugs is used for wash.

2) Add water of the right temperature when diluting stock: D-76
  @60 mixed 1:1 water @76.  Look out for the thermal mass of the
  graduate and the developing tank.

3) On really cold days I use a heating pad under a tray.  For printing
  the pad stays under the developing tray.  Put a folded towel
  under the pad so the pad heats the tray/liquid rather than the bench.

I made a water bath from parts from an old processor: a tank, a heating
element, and a thermostat.

 If room temperatures won't do it try a reptile
warming pad or better yet a seed starter pad
under a tray of water. Dan

A) Leave them in a room at the 'normal' (20C/68F) room temperature for
a few hours...

B) Put the bottles in a large vessel with water in it warmer or colder
than the solutions until they are raised or lowered to the correct
temp. Leave the thermometer in the devloper, as it is not necessary to
measure stop bath or fixer temp if all three are kept together in the
same environment. It also risks contamination. When the developer is at
the right temp, begin.

This is so basic, I cannot imagine you have to ask...