This is the technique that I will generally use. It's not the fastest but I do find that it the most precise (for me). This technique works well with any style of tweezers but my personal favourite is a 75 degree boot style tweezer as I find that they tend to work best for multiple diameters and fan widths. With this technique I feel that creating equally spaced, symmetrical fans is much easier.
Pick Up & Place
How to make the fan
Isolate the number of lashes you would like.
Pick up and place those lashes back down onto the strip.
Quickly wiggle your tweezers back and forth close the base of the lashes to make them fan.
Manipulate them into place individually if needed to create symmetrical fans.
Grasp firmly and remove from the strip.
This technique may not be suitable if you choose a brand of lashes that has little tack to their backing strip. It needs to be sticky enough to hold the lashes in place while you fan. If the strip is not quite tacky enough then you may want to try using a holding bay instead.