I usually clean it up as best I can and let them know the areas where they'll want to grow it out to achieve their desired style. For example, the other day a man came in who wanted to slick his hair back, but the problem was that the front of his hair was too short to slick back and stay in place. So I just cut everything else around it down to that length and let him know it should be easy to slick back for him in a month or two but until then at least his hair would still look good.
Always let them know, they need several cuts to get what they desire. I always tend to dk that. I'll cut their hair to get the shape going. Then when they come again, that's when you get to work & give them what they want.