Your program needs:
-A way to color exactly one pixel at a time.
-Layers that have adjustable transparency.
-The ability to shrink and/or rotate a single piece of the image in such a way that it doesn't become pixilated and ugly.
I will be using Photoshop, so the keyboard shortcuts, tools, and menus that I cite will only help you if you are too. If you're using Paint Shop Pro or another program, you'll have to know them yourself.
1 Make a new document about 100x100 pixels. This document is NOT your edit. Make a new layer, and on that layer, use the Pencil tool (click and hold Brush tool to get it) and draw a little design somewhere on the document like this:
(Zoomed to 500%)It doesn't have to look like that, just so long as it's really small. You can place the pixels any way you like, really.
2 Copy your pixel design three more times and arrange them in a 2x2 square. You can merge the three copies into one layer if you like, but keep one separate so you can easily copy it some more.
3 Copy the design again, and flip it horizontally or vertically. Arrange a bunch of these flipped copies in a circle around the 2x2 square from last step. Merge them if you like, just be sure to keep your original tile.
4 Copy your original, unflipped tile and put the copies in the vacant corners. Merge all your lace layers.
5 If there's anything you don't like about the pattern so far, now is the time to fix it. Erase pixels you don't want, and add in new ones where you think they're needed.
6 Copy the whole lace layer once, and place it alongside the original. Merge them into one layer, then copy that layer, flip it vertically, and place it above or below the first one.
7 Open your avatar edit that needs a lace pattern. Paste your lace pattern on a new layer above what needs to be lacy, and tile it so it covers the whole garment with room to spare.
8 Rotate and/or shrink the lace layer with Free Transform (ctrl+T). This will soften the edges of the lace (and slightly alter your pattern) but keep the regularity.
9 Erase the parts of the lace that you don't need.
10 If desired, change the transparency of the Lace layer. You could also change the color of the lace by means of Edit->Fill (Shift+F5) and setting it to use "Color" which you then pick, and setting the mode to Normal and making sure the "Preserve Transparency" box is checked. After you do that, try changing the layer blending mode to "Multiply" or "Overlay" because sometimes filling with a color other than black doesn't look nice and messes with the shadows, and changing the blending can fix that.
(Adjusted Transparency) (Filled with Color)
