[Casey76]

OK, I couldn't resist and bought 12 strawberry plantlets today.

Should I mulch them immediately, or do I let them over winter first, then mulch next spring just for the fruiting season?

And... is miscanthus (elephant grass) OK for mulching

[sunshineband]

Mulching would help keep in moisture, whether this year or next for fruiting, as well as keeping fruit next year clean

Any dried grass that wouldn't blow around would be fine: some folk use shredded paper, but aesthetically I prefer the look of straw or similar   

A few slug pellets underneath the mulch (organic or otherwise) is a useful precaution

[gavinjconway]

You must also pull any flowers off this year so the plant can grow strong..

[Trillium]

The way the strawberries are grown this year (water, food, etc) is the result you'll get for next year's berries. So yes, keeping their soil relatively moist, well fed and free of weeds will definitely make them yield well for next year. And as Sunny says, add slug pellets cause they love strawbs too unless your summers are drier than the UK. I never do slug pellets on mine because I suspect my dry summers are similar to yours.

You'll also find young runners popping out and these should be limited to a max of two per plant, otherwise the parent plant puts out too much energy making young ones rather than forming the berries for next year.