Plan the route
Get notams
Get airport data
Phone the airport
These days I tend to use Skydemon for everything. I plan the route, and get the plates from their plate subscription along with glancing over the national AIP plates that SD also delivers, and then print everything out.
In fact I flew to France a few weeks ago and the whole pre-flight planning process took about 15-20 minutes. I planned the route, downloaded the notams and plates in SD, filed the flight plan from Skydemon and printed my stuff then off we went. The SD plog was within 5 minutes, the FP's were filed just fine...in fact the only slow bit was the GAR form - It would be nice if you could submit the GAR from SD as well, then life would be really easy.
I didn't phone the airport though.....