Some of the easiest things to do...
Here's a quick check list that you should do before the test:
1. Service your engine...You would not believe the amount of cars that fail on emissions because people don't look after them and I'm not just talking about old rust buckets, I've seen car that are 3 and 4 years old that do the same. If your car expels a lot of blue smoke, your engine is wearing and you are burning oil hence significantly increasing your emissions.
2. Get your engine bay jet washed..If your engine is caked in oil, dirt etc they have been known to reject cars on this basis.
3. Check/replace your windscreen wipers...If they are split, cracked - they've perished, fit some new ones.
4. Get your mechanic to check things like steering bushes, suspension, steering CV-joints while they are servicing your car. If these rubber bushes are perished or the joints are split/leaking, the NCT guys will fail your car.
5. Brake imbalances are also one to watch out for, again talk to your mechanic about checking this.
6. Also get your headlights aligned, this is a 5 minute job that your mechanic can do.
Everyone, feel free to add to this list.
Cheers and happy motoring!
Ciaran