I personally don't know if this is the best way or not, but here's my method of making a pattern.There are limits to what you can do, by staying within the boundaries, you can make some fun stuff.

First I try and use only four colors to make a creation: Red, Green, Blue and Black. The RGB are the three color channels that the TSR Sims 3 Workshop uses. I had to learn the hard way when I tried and made some patterns (which I have uploaded) which are essentially stuck with only one color with various hues.

An example is my "Tiki Jungle" pattern:

Looks pretty good huh? Well heres how it looked after I was done with photoshop:

By using either Red (ff0000,) Green (00ff00,) and Blue (0000ff,) I was able to create a pattern with three different channels that can be changed.

BTW, if you want to reuse certain patterns, make sure you save the project as a PSD. Then you can go back and reuse them like my later example here:

If you want a color to be static, change it to black. The background color will pick it up as a seperate color and it'll turn out good, you just can't adjust it. Here's an example:

By using black, I was able to change the color using the Background tab on Sims 3 Workshop to make this It doesn't have to be white, it can be any color you want. But make sure you like it cause it's always going to be that one color:

If you want to have two different shades of colors here's a rule of thumb: If you want the resulting color to be darker, make it lighter in photoshop. Think of it like a film negative in that sense.

Well I hope I helped at least some people out with making patterns for the Sims 3, It's super fun and helps you fill observed gaps in the games patterns.

-comet65