How can I get my dad to help me clean out the garage?

I have absolutly no idea how someone can accumulate so much junk in such a short time. My dad wants me to clean out the garage my myself, but the only problem is that there is so much junk and alot of it is his. I have tried cleaning out the garage before and I don't know what to throw out, because its all his.
Every time I ask him to help me, he always says he will help me next week or month and when the time comes around he won't help!

Just start throwing things away. If it's important to him he'll start helping just to keep things from disappearing. You might make a big pile of stuff that you're throwing away being sure to include stuff that he'll probably want to keep. Ask him to check it out. If he finds things he wants to keep then he can pick them out. Do this a few times and he'll probably get the message. "Help or lose all your stuff"

Tell him you'll be holding a garage sale 1 week from this Saturday and everything in the garage will be sold or if it doesn't sell, will be donated to the Sally Ann. Anything Sally Ann doesn't want goes to the trash. Then this Saturday start organizing your garage sale. Put price tags on stuff. Make signs advertising the sale and leave them where he can see them. Put up posters at the local supermarkets.

At least proceeds from the sale will help to reward you for all your hard work.

First let him know that you will be throwing away anything not being currently used. My mother had sold her house and needed help emptying the attic and the garage. My husband just threw away everything that was stored in both places, except of course any papers since he didnt know if they were important or not. Took him two afternoons to bag everything up and get it out to the curb to be collected by the garbagemen the next day. No time for remorse that way.
If your dad doesnt show up after you've told him that things will be thrown away, then he must not have anything really worth keeping and is probably considered garbage anyway. Just keep any paperwork that you find.

Pick a Saturday two or three weeks from now. Put a big piece of neon posterboard up on one of the kitchen cabinets (where he will see it everyday). Write the date you picked on the posterboard and the message that anything of value that is not removed from the garage by this date will be disposed of. When your cleaning day rolls around go into the garage armed with a box of contractor grade green garbage bags. Load'em up! Put'em curbside. Mission accomplished.

The US Navy has a solution for this. It's called "gear adrift." Basically anything that's not in right place is trashed or otherwise disappears.

Maybe start by finding a big blue tarp in that mess somewhere. Put everything you think is junk into a pile under the blue tarp, tell your dad that you consider the pile junk, if he's interested go through it, and stick a sign out front, "Garage Sale Here (two weeks from now)." Anything that's still under the tarp goes into the garage sale.

Video yourself throwing his car keys in there.. right to the back. Then offer to help him find them.