I like the look of the Khandish forces in GW's Lord of the Rings miniatures range. But they sat unpainted on my shelf for years because I found the idea of painting the little star logos on the banners (both sides!) so daunting.
But I found some videos on YouTube about making your own decals, and realized that this might be the solution for my Khandish warriors. I gave it a go and it turned out to be pretty easy, and I was pleased with the results. So I thought I'd share what I learned in the process.
(Click on any image to see an enlargement.)
You need some sort of way to create the images that you'd like to use as decals. I chose Inkscape, which is a free vector-based drawing program. The advantage of vector-based programs is that the drawings you'll make are more easily and accurately resizable than bitmap-based programs. And free is hard to argue with. But if you're more comfortable with a different program, I'm sure it would work fine. I think you'll struggle to get good results with Microsoft Paint, though.
You'll also need an InkJet printer. These are pretty cheap and common these days, and even if you don't have access to one you can probably get your decals printed at an office supply store.
Lastly, you'll need special decal paper and a sealant. I found mine at Amazon, Testor's brand paper and the corresponding sealant. Other brands may work, perhaps even better, but I only have experience with these products.
I assume you already have a sharp hobby knife, a small shallow dish to hold some water, and a small stiff-bristled paintbrush.
I can't give too explicit instructions on drawing your decals, because I don't know what you images want to create or what software you're using. But I can still offer a few tips.
First, try something simple. My Khandish star insignia are about perfect for this; I'd hold off on trying the Banner of Minas Tirith until you've already racked up some experience.
I found it hard to gauge on the screen exactly how big the decal would be once printed (yes, despite the rulers and grid). So once I had my star design, I put several size stars on the page and printed it. Of course you should use regular paper for this, not your valuable decal paper! I could then compare the printout directly against the figures. Once I determined which size was best, I deleted the others, and then at that point it was safe to duplicate the image as often as it would fit on the page. Since you can only use the decal paper once, you might as well fill the page up.
Although you're going to need dozens and more of any decal designed for line troops, I found it hard to gauge exactly how big the decal was once printed (despite the rulers and grid in the drawing program). So once I had my star design, I put several sizes on the page and printed it -- and of course you should use regular paper for this, not your valuable decal paper! I could then compare the decals by size directly against the figures. Once I determined which was best, I deleted the others, and then at that point it was safe to duplicate the image as often as it would fit on the page. Since you can only use the decal paper once, you might as well fill the page up.
Since my decal paper was half size, it took some experimentation to get the orientation correct in my printer. Since the decal paper is also relatively expensive, I economized by running tests with regular printer paper cut in half. Write "front" and "back" on the two sides of the test paper, and run test printings on those scraps until you're confident that you have the right print dialog settings and paper orientation.
With your drawing and printer ready, you're now ready to make a real printout. Remember to use the highest quality printer settings. Let the paper dry overnight. Then spray a coat of sealant over the decals, and let that dry overnight, too.
Prep the area on your figure where a decal will go by basecoating in white. I originally tried using a light brown, thinking that would be do, but the decal colors are not strong enough and the yellows of my stars were displeasingly dim.
Then get a small shallow container and put some warm water in it. Now, assuming you're going to apply more than one decal, jump start an assembly line by cutting out one decal and put it in the water. Then start your assembly line proper: let the decal in the water soak while you cut out another decal, put the new decal in the water, take the now-soaked decal out and apply it. Lather, rinse, and repeat.
For best results, you should cut as close to the edge of the decal as you can. But that seemed too time-consuming to me for my stars, so I just cut out the octagonal shape enclosing the star. Once covered with paint, the final results were still satisfactory to my eye.
There's a bit of an art to actually applying the decal. Try holding the wet decal between your thumb and forefinger, and slowly slide them in opposite directions while gently pressing them together. You want to see or feel a little slide where the decal moves a bit, leaving a small bit hanging off the edge of the backing paper. You can then use a finger or a wet paintbrush to pin down that edge on the model, and slide out the backing paper out from underneath. Use the wet paintbrush to push at the edges of the decal to orient it and/or slide it into place if neccessary; then "paint" water over the outside of the decal to push the decal firmly down on to the model's surface. You'll need some persistence if the area you're trying to decal instead very flat.
With a little experience, you can get a good rhythm going in your assembly line. I managed to decal a box of Khandish warriors (ten figures, front and back) in about 30 minutes. That's a huge savings over the time that hand painting the insignia would have taken, and I'm quite happy with the results.