Mashed potatoes

[CarrotPuff]

How do I make a mash that is not lumpy? Is there a secret... I don't particularly like it myself, but make it now and again for kids, and it always comes out with lumps. What am I doing wrong?

[PickAChew]

I've tried the aunt Bessie's, tesco and sainsburys frozen mash. The tesco was vile - tasted processed - but the other two were lovely.