Just to add to what Paul has said, I'd recommend applying it in nice thin coats. I use a fairly wide, flat brush and build the Klear coat up in 3 coats prior to decalling. Applying the Klear too 'wet' will cause it to fill in the panel lines and set in them, which will make it harder to highlight them later on with a panel wash. Also, I rub down each coat of Klear with some micromesh- start with 4000 and then 8000. This smooths the coat out and also adds a little to the shine. Then, once the decals are on, a final thin coat to seal things in. I'd then spray a matt coat after (optionally) weathering the model.