For those that are looking into doing some designing for digital scrapbooking, here are a few tips I have learned along the way (sometimes the hard way):
1. Look at other designers, their dimensions, what works and what doesn't. Some offer papers that are square and rectangular. Some square sheets can't be stretched or squished into a rectangle without messing up the pattern. I rarely make 8 1/2 x 11 papers. I have a post about dpi on my other blog.
2. Alphas - I offer more than one usually. I like to mix and match them in a layout. I will use patterns to match the papers or the solid colors from the palette. Occasionally I'll make the letters separately and include the alpha back instead of making them all one, this adds to the ability to mix it up.
3. Elements - you want them large enough but not so large your "customers" have a hard time using them on a slow machine. I try not to go smaller than 600 these days (but earlier kits are smaller). I've made ells as large as 1800-2000.
Use palette generators, photos and other kits for inspiration. I sometimes scrap and need a kit so I make it and other times I just make a kit based on a color palette I love. I've also made kits because I saw something I liked but wanted something a little bit different (maybe in pattern or coloring). I've polled my readers asking for suggestions. Some days I'll play with papers and my graphics programs. I will either upload the paper paks or some time down the road pick a paper and make a quick page or mini out of it.
I try to make kits that can be off-theme, in other words, if it's a boys kit I make sure there are parts that can be used for anything. I make sure that those girlie kits can be used for boys layouts too (I am a mom of 4 boys, stepmom of 3 boys, have a stepdau, a goddau. and a godson). This is a good thing to remember if you are going to be into selling your kits.
That's all for now.