I find studying photos of my class boat being raced is a good way of seeing how 'fast' and 'slow' look. This works for anytime of year but it keeps your head in the game during the winter months.
It helps because you can make a mental note of what you should look like if you are doing it right. You don't get as much as maybe seeing video footage but you can check out the sail trim, boat trim, the crew positions, tiller position, all that kind of stuff. It is helpful if you know that the picture is of one of the class leaders but sometime just comparing two photos of boats tacking you can see which one is going to be quicker can give you pointers as to what makes a boat go faster.
For example check out these two pictures of boats tacking in what look like not too dissimilar conditions:
The one on the top is the faster; the mainsail is filled, the rudder blade is central and look at the crew position and movement! These guys looked to be moving in sympathy with the boats roll and look like they will come out of the tack with good acceleration. The rudder blade on the boat on the bottom picture is going to act as a brake, the mainsail is not filling and the crews movement looks uncomfortable by comparision.
Sometimes, when there is more than one boat in the frame, I like to try and think through the scenario as best as I can deduce from the picture, and ask myself what I would do if I was one of the boats. This one for example:
Supposing you are the blue boat sailing towards the mark. Do you pinch to lay the mark or tack? What would you do?