A lot of the people I meet are stuck in the same old training routines. If you are trying to progress and get results with your training this is one of the biggest mistakes you can make.
You body will quickly get used to the new stresses you put on it and will find it easier the more it does it. This means you will not be getting as much out of your workout.
Training should always be progressive and you should always be thinking of ways to mix it up.
For example if you do a 5 mile run each time you train, try changing it to a interval session. Basically this means a hard work period follow by a rest period. A simple version would be running flat out for 1 min followed by a 1 min rest.
If you weight train try changing the order of your exercises, including new exercises or shorter rest periods. Off course changing your training will depend on your individual needs and what you are trying to achieve.
Circuit training is another great way to mix it up. Next time your in the gym try doing a PHA (peripheral heart action) circuit. This can have hundreds of different formats. One idea would be: 2 min row, forward lunges, press ups and lat pull down. This will shunt blood all over your body keeping your heart rate high through out the circuit.
As you train keep you eyes open to all the different things you can do. Everything from using free weights, balance boards, med balls, swiss balls or kettlebells can all give you amazing results and keep your training fun and entertaining.