Stopping in the wet

Make sure the blocks are correctly positioned too. This can make quite a difference.

Going back many years the block compounds were different colours - black which were harder was suitable for dry weather and red which were softer was suitable for wet. Using red blocks in the summer just wore them out faster.

I remember swapping the blocks - or at least using red blocks on the winter bike.

Hope this helps.

clean your rims too, give the braking surface a good scrub. a bit of emery board out of a puncture repair kit is good for roughing them up a bit and giving your brakes more bite, careful you don't sand your tyres though

Shouldn't be any problem in the wet with V-brakes.

You don't want them to bite too soon. The bite point should be where the levers are reasonably close to the bars, where your fingers have more power (but obviously not so close that the levers can touch the bars).

Otherwise I second what purplecup said. The compound in the blocks can make a big difference in the wet.

changing the blocks can make a whole world of difference - what blocks are you running now?