First thing you need to do is call an electrician out to your house to see if your electrical panel can accept the increased load.
Depending on which model you are looking at, some run on 115 volts and some need to be hard wired for 230 volts.
If your panel cannot supply the needed power, now would be the time to talk to the electrician about upgrading your breaker panel.
Next you will need to find a suitable location in your yard.
If you are thinking about putting the spa on a deck, you must make sure that the deck is structurally sound and can support the additional weight of the unit and don't forget the weight of the water and the occupants inside.
The supporting surface must be perfectly level; they will not work properly on a sloped surface.
If you are going to put it on the ground, a concrete slab would be perfect.
If the area does not have a secure pad, consider building a pavestone slab, but before you put down the stones, be sure to run the conduit wire.
After you have determined that your house can have a hot tub, you must figure out which model will work best.
The less expensive 115 volt models do not allow for the jet pumps and the heater to be running at the same time, so if your family lives in a cold climate or you soak in the water for an extended period of time, you may want to consider upgrading to one of the 230 volt models.
Some of the more basic versions have only one motor, while the high end ones have a dedicated circulation motor and separate jet pumps.
Size needs to be discussed, if the unit is only going to be used by a few people at a time, a smaller one will work better, but if the family size is larger or you like to throw parties, you should look into the larger ones, nobody likes to be cramped in a relaxing spa.
Remember that the larger the spa, the more energy it will use.
Options will be the next item on the list, and now day's hot tubs come fully loaded.
Do you want a single light or the full LED color changing system.
The number of jets will depend on the size of the unit, if you are using it for muscle relaxing purposes; make sure to get one that has the jets in just the right spot.
Depending on which brand you get, stereos can now be installed, just be sure the kids don't disturb the neighbors with all that music.
Many spas come with synthetic materials which will last longer.
Insulation is a very important factor; get the full package so that the unit uses the least amount of electricity.
Safety is a huge concern, especially around water.
If there are going to be kids around the area, you may want to think about building a fence to keep them out.
Make sure to get a cover that is ASTM rated, if your pets like to sit on objects, upgrade to the reinforced ones.
Hire a professional to wire up the electrical.
Most important thing is to enjoy your new found relaxation.