First: You need the right tools. Tongs, serrated pairing knife, a fork, and a cutting board. The tongs can be used to pick the fruit off the cactus. Look for fruit that is bright purple or deep in color. It should come off fairly easily with a little twist. You also want to see purple on the stem of the fruit when it comes off the cactus. This will yield the most juice.
Step 1: Hold the fruit still with a fork.
Step 2: Slice off both ends with your knife.
Step 3: Slit the fruit down the middle, just enough to cut through the skin.
Step 4: Slide your knife under the skin and peel back to reveal the fruit.
Step 5: Continue peeling back the skin and place the peeled fruit in a bucket/bowl.
Step 6: Let the fruit sit overnight in your fridge. I find this helps the juice come out.
Then you can pass the fruit through a fine mesh strainer or a tea strainer and you have your juice! No prickles and not too much work. Plus, you can skip buying the 400 dollar juicer for your summer fix.
I freeze the juice too and am making popsicles this weekend... Good LUCK!