HIIT is a great form of training that can be done anywhere and with minimal equipment. To do a HIIT session at home you first need to decide what kind of training you want to use. There are many options. You could use running on the spot, an exercise bike, body weight training, weighted exercises or running up the stairs. Any activity that you can do at a high intensity will suffice.
The next task is to decide how long your intervals are going to be. The best way to decide this is to perform your chosen exercise technique or discipline for as long as you possibly can. The intensity should be high, for example think more of sprinting on the spot rather then jogging. When you have your interval length you need to decide on the rest period length. This should be long enough to allow you to sufficiently recover between intervals. A good starting point would be to have a rest period that is twice as long as your interval period. However clients with higher fitness levels will likely want shorter intervals. The shortest your rest period would want to be is 25% of your interval length. So If your interval is 4 minutes, your rest period would want to be no shorter than 1 minute. The number of intervals you do is completely up to you and should be determined by your fitness level.
Aim to train 3 to 4 times a week. Change the training type you are using every 6 to 8 weeks to keep your body guessing. This will ensure you get the quickest results.