The symptoms of jet lag will naturally get better as the body adjusts to the new time zone. However, recovery may take 1-1.5 days per time zone crossed and there are a number of ways in which you can try to speed the process up.
You can start the process of adjustment before you even leave home by changing the time at which you go to bed and get up. If your journey is eastward, for example from the UK to India, you could move your body clock forward by going to bed and getting up an hour earlier. Similarly, if you are travelling westward, for example from the UK to Canada, you could move your body clock backwards by going to bed and getting up an hour later. You should not attempt to re-set your body clock by more than 2 hours before you travel.
If you have a choice of different flight schedules and arrival times, a late afternoon or early evening arrival might be better, since you can "use" the tiredness due to travel fatigue to help you get a full night's sleep in the new time-zone.
Many travellers find it helpful to set their watches to the time zone at their destination as soon as the flight begins. Depending on the time of your flight, you should try to get some sleep during what would be night-time at your destination. The timing of meals is another cue that helps readjustment of the body clock, but most people have little choice in the timing of meals on the flight. Although the timing of meals can help to synchronise human circadian rhythms, there is little evidence that the content of meals, such as a diet higher in protein or carbohydrate content, speeds up adjustment to the new time zone.
If you are only travelling to a new time zone for a short period (less than 48-72 hours), it may be better to try and avoid adapting to the new time zone by staying on your home time. You should try to make sure that you eat and sleep at your normal times - if you are having difficulty getting as much sleep as you need, try to have a nap in the early afternoon after lunch, when you will naturally be sleepy. If you are travelling on business, try to arrange any important meetings for times when you will be more alert - during the local morning if you have travelled westwards or the local afternoon or early evening if you have travelled to the east.