I usually only call the hotel: first a couple of days after I made the reservation in order to check if they have the correct information and put in a request for upgrade. One day, or a couple of days, in advance of the actual stay I usually call again to do the same.
Until now most hotels have been very cooperative, results have varied (of course) but in general I've received at least upgrades to exec. level, even on Priceline stays (BTW I'm a HHonors Gold).

The only time I had email correspondence with a hotel before the actual stay, was when the concierge contacted me to ask if I had any requests. Very much appreciated action.