1. Wash your clothes inside out
It's much less soul-destroying if the bobbles are on the inside, not the outside
2. Wash on a short, delicate cycle
You want the jumper in question to be spun around as little as possible, so keep things short and sweet.
3. Use gentle, liquid detergent
Hard, powdered detergents can rub up against clothes as they're dissolving in the washing machine, so a liquid option is always best.
4. Wash separately
Keep delicate clothes away from your other, harder clothes. If they rub up against each other, there's only going to be one loser.
The gentlest way to wash any of your clothes, special handwash detergents can be bought from your local supermarket.
6. Air dry your clothes
Ignore the drier at all costs - heat and friction causes pilling, so avoiding this where possible is the best prevention.
7. Brush regularly
The garment (not your teeth), using a lint roller or special garment brush.
8. And if pills do appear
Try using an electric fabric shaver on the most delicate setting, rather than scissors, which could be more likely to cause damage. Or, take one of your own razors and set to work - just make sure you're VERY careful and work in good light.