Hi Andy,
If you are trying to square up a piece of wood, I would suggest that you are better off doing this on the bench top rather than in a vice. That way you can hold the plane so that the fingers of your left hand (assuming you are right-handed) can act as a fence on the side of the wood. That will help you to control the plane better. If you have trouble planing against a stop, with the wood moving about, you can clamp it at both ends with something like the Veritas wonder pups and dogs - see here
http://www.brimarc.com/home.php3?page=p ... c=C_106_14
Only clamp the wood lightly so as not to distort it.
Use a straight edge (a 24" metal rule would do) to check whether the wood is straight in its length. If it's not, mark the wood where the high spots are with a soft pencil. Plane the high spots away - keep checking and marking with the pencil until you get there.
You also need to plane flat across the width. What you need to watch for is whether the wood has any wind (or is twisted). You can check this with a pair of winding sticks. Get two bits of wood about a foot long x 3/4" x 1" (dimensions not critical). Lay these on the wood one at each end and sight along them - they will emphasise (because of their length) whether the wood is twisted. If they are, as before mark the high spots with your pencil and plane them away.
That will deal with one face of the wood. Have a go at that and see how you get on.
One thing I find helpful with all this is to plane slowly and keep your eye on the mouth of the plane. That way you can see where the blade is taking the shavings off and make adjustments as necessary.
Hope this helps - let's know how you get on :wink:
If all else fails, get hold of David Charlesworth's DVD. It really is good :wink:
Paul