I'm sure there are a dozen easier ways to do this, but this is what I do... I make one motif of every color scheme I want to explore. This also helps me refine the written instructions and tweak the design while I re-make each one. Then I lay them all out together and photograph them. I print it out small on plain paper. (I think some people just paste them in PhotoShop, but I don't do that). I'll print out 5-6 or more copies. I cut them out so that each motif is on it's on piece of paper. I think these are about 1.5" each. Then I lay them out in several different configurations, and usually take a digital photo of each new composite. (I can delete the unwanted ones later and I can look at my camera's viewer to be my "guide" where to put the motifs later! Or how to make a diagram for my written instructions). Below is the one I ended up choosing. I ended up omitting one of the five motifs above. The one on the bottom right of the five above is the one I decided not to use. I just was too boring compared to the others. When I make motifs that are different, I try to look at each one individually and make sure it is really, really nice, even if used alone. If it is weak on it's own, then it's too weak to be included.
When I made the color schemes for the above swatches, I tried to alternate light/dark/medium values. I didn't want it to be unbalanced, all dark over here and all light over there....
When I do a submission, I will make a color copy of this composite photo below, and include it with my proposal to show the buyer what it is going to look like when it's done... without me having to actually make the whole thing.
It also helps me guess how much yarn I am going to need by figuring out how many squares total I am going to have. I can make an educated guess how big the final project will be. I don't remember if I did this with this particular project, but I could have taken apart the one unwanted motif color scheme and measured the yards used for each row. If row one is 5 yards times the number of motifs plus some for edging.... you can do the math. Then you look at the number of yards per ball of that color and divide to find out how many motifs you can get per ball.... and add a ball for good measure, for edging, and in case there is a flaw in the ball.