Here are a few tips for helping you tactically at the windward mark. First, never come in on the port-tack layline. Why not? Several reasons - you may not be able to get around the mark with a wall of starboard-tack boats going around it, you'll be heavily blanketed by boats that are going downwind already, and you won't have much time to set up for a good mark rounding and spinnaker hoist.
Windward Mark Roundings
Instead, tack onto port a good 5 to 10 boatlengths from the port-tack layline. Then, you can tack onto starboard at the starboard-tack layline and have plenty of time for the rounding, as well as rights at the mark.
It sometimes pays to overstand the starboard-tack layline. This is especially true when there is adverse current sucking you towards the mark, but it also makes sense if there's a pack of boats on the starboard tack layline. Almost always, there's that one boat in the inside of the pack inside the two-boatlength circle with rights on everyone. They're pinching like crazy to try to make it around the mark, and cause the whole group to pinch like crazy to avoid hitting the boats to leeward. If you had overstood the mark slightly, you can easily sail around the group because you won't be pinching and will thus be moving much more quickly.
Before you go around the mark, know where the next mark is and have a plan for the next leg. If you're going to go downwind to a leeward mark, do you want to jibe as soon as you get around the windward mark? Is there an offset windward mark that you have to go around? Is there current sucking you away from the jibe mark, so you should stay high? If you know what is going on before you go around the windward mark, you won't suffer any confusion immediately after rounding.
When you do round the mark, use your weight and the sails to help you turn and bear off. When I first started sailing Lasers, I had terrible windward mark roundings - I couldn't seem to bear off for the reach or run, even though my rudder was cranked way over. However, I soon learned that by heeling my boat to weather and dumping my mainsheet as I went around the mark, I could easily bear off onto the correct course without using much rudder at all. I sailed less distance, and rounded faster. So, as you round the windward mark, hike out hard to weather to help your boat bear off. On a Laser or Opti or any boat with only one sail, be ready to ease the sheet out as you try to bear off. On boats with a main and a jib, leave the jib in tight and blow the main - the wind's force on the jib will help push the bow down.