I've managed to get hold of an old GW hill, but can't find any guides on how to finish it At the mo my only guide is the box. The box art is a pretty uninspired showing the hill apparently covered using GW static grass . But do not have one of those static generators, So that prob a no go. I do have various shades of flock. Any other advice ?

If it has a rough texture ingrained, then you could just paint brown then drybrush light brown, if no texture, then add modelling sand and repeat the painting steps.

As for grass, it works well in patches of varying size, it is really hard to get it looking natural, but in my opinion, static grass looks 100x better than flock at 25mm scale and you don't really need a static generator.

Static grass by itself doesn't add a lot of variety so try some or things in addition such as bushes, or small rocks, shrubs etc

A static grass generator makes the grass stand up, like real grass and gives a much enhanced effect. It can also then be drybrushed to give a more realistic effect.

If you do not have one and use the static grass anyway over large areas it will not look realistic. The fibres will lie down in a random manner and drybrushing becomes difficult.

In which case I would go with various shades of turf or flock and add plenty of bushes and even trees. There are all kinds of products such as clump foliage or lichen. Path ways can be picked out with earth blend turf. Be creative and it will still look good.