can anyone give me the best way to higlight models

personally, i find the best way to highlight is like this

take a very very fine brush (army painter insane detail works pretty well for this)
slightly thin out the paint you're using (if its GW paint, 2:1 paint:water)
apply very thin coats where you want the highlights, do this 2 or 3 times depending on how intense you want them, a couple more may be needed if going over a very dark colour like black or necron abyss


or, something else i found effective, is basically doing things backwards

for example, the boots that marine scouts wear, i find it easier to paint them a lighter colour, and then use a darker to fill in the gaps leaving only the areas i want highlighted showing


hope this helps

A top tip for edge highlighting is to angle the brush at about 45 degrees to the edge you are highlighting and work it along the edge. You should always, as Talus says, thin the paint down, this goes for base coating as well.