When I was a child & my jeans or my brother's pants needed patching, my grandmother would iron the patches in so they were on the inside facing out (usually before the fabric was able to fray in the wash). This made them less obvious, virtually invisible, if done right, than the traditional patches thing on the outside, particulary when we were able to match the paches to the fabric color. I still had some of the outside type of patches, but these were emboidered patches, added for fashion statements & not often used to cover actual tears, especially once I found that they weren't as sturdy as the real thing.
I decided to use my grandmother's technique on my husband & son's jeans in a way that strengthens the jeans & keeps some of the great texture of the frayed fabric, while adding a new textural detail of its own.
Starting with some bits of vintage 60's denim fabric that I had lying around, I pinned the fabric to the inside of the pants & basted around the edges to hold to fabric on straight while I stitched. Any fabric could be used, you could even use lace or velvet, for a pretty contrast. Since these jeans belonged to my husband & son & they were signifcantly damaged, I decided to use more of a matching fabric. If you're trying to strengthen the area, as well as patch the hole/s, I'd suggest matching the fabric to the weight of the pants fabric. If you want to use lace on heavier pants, with large holes, you could try backing it with another fabric first, even if that fabric is sheer, for extra strength & to help keep the lace from tearing, when the pants are worn.
Once the patch had been basted to the inside of the fabric, I started stitching, back & forth across the patched area. This is amost like weaving extra stability into the area. The stitches don't have to be perfect or perfectly even. These patches look great stitched with a more 'primitive' look, it matches perfectly with the frayed edges of the fabric. I used a blue thread (also something vintage that I've had lying around forever), that is similar, but doesn't quite match the patch or the original jean fabric, to make the stitches stand out a bit, for texture, but not too much (for my husband & son). You could use a completely contrasting thread, to add another layer of texture to your design. Sewing the stitches in more than one direction, crossing over each other, strengthens the area, along with adding a design element.
I like how these patches turned out. It takes a while to do patches this way & I used up the better part of a day for each pair of jeans, but I think it's worth the effort. If you don't like hand stitching (I find it kind of relaxing), you could try machine stitching. The effect would be a little different, less primitive, but still interesting. Maybe you could even use different stitches or embroider a pattern over everything...