Use the FAA's site.
First start with the airframe (make, model, & serial number) Print them
all. READ them thoroughly to insure that your plane is either included or
excluded.
Then do the same for the engine, engine accessories, avionics, ect.
After you've done that, use one of the commercial online services that will
sell you a one time search & report. Use this to cross check your own
research. You may find that they pick up some that you didn't and you may
find that you pick up some that they didn't.

Make an index listing each AD number, a description, and if it's recurring
or a single event.

Now go through the log books of the airframe and power plants. Make a list
of every AD and Service Bulletin mentioned, the book, and page number where
it was recorded in the logbook. In many cases if a SB has been complied
with it may qualify as compliance with a later AD.

When you're done, keep all the records in a 3 ring binder for reference.

This is the method that I used to research the airplane I flew for my CFI
and II. It made that part of the checkride last all of 5 seconds each time.
It's also the method that I used when shopping for our Aztec, I keep the
binder for the plane we purchased up to date to present it to our A&P-IA
during our annual.

Jim