So you want to be a dad; this list is here to help prepare you. Here are some ways to get ready for it - specifically for child ages 1-5, please add suggestions for me and others for whatever age(s) you have experience in....
  1. Get a puppy
    Seriously, you need to have a puppy and take care of it for a while before trying on a human baby.
  2. Cold food
    Eat all meals cold, usually standing. Bonus points if you include holdings the 10-30 lb. bag. Work your way in to eating leftovers only, like a few fries and a third of a cheeseburger and one chicken nugget.
  3. Balls
    Pick up a bag weighing anywhere from 10 to 30 lbs, with both hands, and then inflict pain upon your misters in whatever method you choose: run in to the corner of a table, have someone knee/punch/kick you, etc. The key here is DO NOT DROP THE BAG. Do this for 3 to 7 years (your mileage may vary, depending on number and size of children).
  4. Staggered sleep schedule
    Set your alarm for multiple, random times throughout the night. Get up and do a crossword puzzle, then try and go back to sleep. The goal here is to function on short intervals of sleep, perform a task that requires brain function once unexpectedly awakened, and be able to go back to sleep ASAP. Do this for a week to start, build up to a month
  5. Forget conversations and long sentences
    Learn to communicate via text and/or short bursts, with gaps in between. Bonus points if you can have someone interrupt constantly, but this is hard to simulate and you'll get there soon enough.
  6. Get mechanically inclined
    Volunteer to put people's IKEA furniture together, build Lego sets following the instructions. Starting at the baby shower going forward, you will have to assemble and fix a never-ending list of stuff.
  7. Do everything in the bathroom
    If you don't have a lock on the throne room - get one. Start doing things that require any concentration in there; emails, texts, ListApp, reading, web searches.
  8. Learn to do things in short bursts
    Naps are gold and must be used wisely. Work on doing the laundry/dishes/lawn/wife in an hour or less, and sometimes have tasks be stopped abruptly without being completed.
  9. Start playing with toys
    As an adult it's viewed skeptically- but as a Dad you get to play with all kinds of toys again. Start practicing (with permission, of course).
  10. On the floor
    Practice getting down on the floor and back up, multiple times a day. Bonus points for having a dog or someone throw the 10-30 lb. bag on to you when you're not prepared.
  11. Distraction
    A core tenet of parenting - getting an upset child distracted and on to something else is a skill. Try it on your puppy.
  12. Get used to bodily fluids
    Pee in a cup and spill some on the floor, or have your wife/gf do it - you clean it up either way. Progress to vomit and 💩 if you're up to the challenge. Have a Boxer (dog) or any other slobbery breed lick your face.
  13. Drive distracted
    Like Ricky Bobby, you should drive with a live mountain lion in the back seat. Too dangerous? Have your wife blast the radio at weird times. You will never drive in a quiet car unless you're alone.
  14. Give away all your money. Take 2 or 3 $20 bills out of the ATM daily and drop them along the sidewalk on your way back home. This will prepare you for when those kids reach their teenage years. Then repeat with $50s and $100s to prepare for college. Continue for 25 years. Then remember: money is overrated and children are forever.
    Suggested by @andersun