First, always be nice and don't "expect" anything more than what you are guaranteed. Next, some ideas to help:

1. Call the reservations line up and find out the hotel GMs email address. Send him/her an email letting them know of your upcoming stay and how you are looking forward to it. If you are traveling with your wife or family, or if there is a special event, put it in the email. The GM will most likelly just pass on your email to someone else in the hotel staff, but since it will have come from the GM, that can often loosen some of those iceburgs up a bit.

2. When talking with the front desk staff, always have a smile on your face and try to find a way to get them to laugh at something. If you can get them to smile back somehow, they are probably now actually paying attention to you as a person, not just an inconvience to whatever they were doing previously.

3. I don't know if this helps or not, but when making an online reservation, there is a comment field. I have seen others here mention that they put a request for a room upgrade into that text box. It can't hurt to put it in there and may help.

4. I personally prefer to checkin when the front desk is not very crowded. It is a little easier to engage and talk with the front desk persons. So if you have any control over check-in time, you may want to try to stay away from morning checkout times and early afternoon heavy check-in times.

5. It probably wouldn't hurt to call the hotel earlier in the day to "verify" your reservation and remind them of the upgrade (or any other) requests you have made.

6. If traveling with family (especially young kids ) bring them along with you to check in. My upgrade rates when I have my daughter with me is much much higher than when I'm by myself.

HTH.