on my board do i leave the daggerboard down all the time and when do i adjust it or put it up. cheers

The dagger board gets you up wind in light wind conditions.
In strong winds it will push the windward rail up slowing you down and making the board hard to control.
You'll soon know when it's time to decrease amount of dagger board in the water.

It can depend on what type of board you ride. On my raceboard, I keep my dagger board down in all wind conditions when going to windward. However on a reach or going down wind. I raise my dagger board as the wind increases. A good rule is in non planning conditions, keep the dagger board down and in planning conditions raise it. Also note that the lift from the daggerboard will help you get on plane so I put the dagger board halfway down to help get on the plane in slightly sub par planing conditions. It sounds a bit onfusing, but the best thing to do is experiment.

surely miss riding one with a daggerboard especially on a Mistral Equipe..fun to ride the rail on an upwind reach and being able to see it underneath..fun!

What sort of board is it?

The above comments are generally on the money.

In light winds keep it down generally.

Heading upwind keep it down generally (more raked back as the wind gets higher maybe).

Planing and reaching have the daggerboard fully retracted (or maybe 3/4 retracted if borderline planing).

Daggerboard down helps learning turning in the very early stages of learning to windsurf by giving lateral resistance.

Clarence