While the tactical principles are similar in all sailboats, the relative importance of keeping your air clear, speed versus pointing, being inside at the leeward mark, etc. varies with the characteristics of the class, the sailing conditions, and the performance of the boat.
In light air, the 505 does not increase speed through the water much when footing, but it does in any breeze. If a boat to windward is threatening to drive over you, and you cannot sqeeze them off, foot slightly to gain separation and clear air. Once ahead of abeam, go back to point mode.
The 505 can also point high - pinch if need be - to climb off a boat to leeward. Just squeeze up a little to gain height, and come back down to close hauled before losing too much way. You can scallop up provided you do not lose too much speed. Sheet the jib harder and tighten the vang to help do this. Work up just enough to be out of disturbed air, then get back up to full speed.
Eyeball the reach angle and consider windshifts on the beat before you get to the mark to determine if you will hoist or not. If in doubt, whip it out! You can go part way down the reach, then douse the spinnaker and two sail reach up to the mark. If you only have to go high for a short distance, you can simply uncleat the spinnaker halyard, not bother dousing, reach up, and then bear off and rehoist.
There are two approaches to the hoist that will keep you in the passing lane:
Keep your air clear for most of the reach, unless the reach is too broad. On a normal reach you can change from "stay high" mode to "get down to the mark" mode as you approach the gybe mark. If the reach is broader than it should be, and people have to work lower to get down to the gybe mark consider the following:
I try to gybe so I come out of the gybe closer to the mark than when I start the gybe - it is SO important to come out of the gybe high and in the passing lane. Perhaps the easiest way to think about it is that you want to gybe slightly early, so you approach pointing a boat length or so above the mark - leaving room for your boom, and exit the gybe next to the mark.
If in traffic, hike hard and sail as high as you can while the crew gets the pole on the mast (you could also acquire a pole launcher to speed this move up). A half a boat length of height at the mark could be worth lots of distance and boats later down the reach!
You must practice your spinnaker douse until you can do it well repeatedly, and know instinctively how close to the mark you can come and still have time to douse. You may have to carry it a little later than normal to fight off an overlap, but remember that you are better off rounding ready to sail fast upwind with someone inside you than you are rounding with no one inside, and the spinnaker only partly doused! If you are not threatened, take down slightly early to ensure a good rounding, and that you are pointing high and up to full speed upwind as soon as you have rounded.
If you are having problems with the douse or setting up the boat REMEMBER to round the mark and point the boat upwind! You are better off going slowly toward the windward mark, than sailing away from it while trying to complete the douse.
Try to come out of the leeward mark rounding as high as possible. If you can make a smooth turn and flatten the boat as you turn, you can luff up higher for a few moments so as to be slightly above the line of boats ahead or astern. This tactic may also force a trailing boat to bear off below you to avoid hitting your transom, putting them in your disturbed air. This can be accomplished by steering the boat at a point a boatlength or two below the mark, and then not turning too fast. You want to be close hauled as you pass the mark.
If you are trailing a boat, force them to carry their spinnaker too close to the mark, and hope they flub the douse and rounding. With a good douse and rounding, you can sheet in and sail right through their lee, while they are completing the manouver and have not set the jib or main properly. Even if you cannot pull of that move, you may be able to tack away immediately, before they are ready to tack and cover.
I believe you can live with a slack vang for a few moments - pulling the bridle mainsheet hard controls the leech, but that having the jib too tight or too loose would prevent you from getting up to speed after the rounding.
Giving away distance at the leeward mark is probably the most frequent mistake I see on the race course.
In very light air, sailing quite high to keep flow over the spinnaker can work quite well. As the air goes from very light to light, sailing low can work very well. You can even sail by the lee with the board right up to slide down to a mark. Somewhere above 15 knots or so, sailing high angles to get the boat planing fast becomes effective, and in big breeze, the top sailors are usually going down the run with the crew on the wire and the skipper fully hiked. The fastest angle may be almost as high as the reaches! Practice your run-to-run gybe technique till it is smooth, and then be prepared to gybe for any puffs, angle changes (and even wave patterns in light air). Puffs are key, the difference in boat speed due to a puff is quite significant.
In many conditions, pumping on waves is VERY effective. Work on your pumping technique and timing, as badly done pumping is quite a bit worse than no pumping at all.
The medium sized flatter spinnakers optimized for reaching do not seem to go as low as the fuller spinnakers, so you may not be able to sail the same optimum angle as competitors near you.
Much as pointing higher upwind is a big advantage, being able to work low of competitors while maintaining speed can be devastating on the run. My crew and I often sit astride the centerboard trunk - motorcycle seat style - as we can lean to one side or the other to steer and balance out the helm, and the slightest puff or shift is more easily noticed.
In a bag boat, if you set up so that you can gybe to port just a little before the mark, you can do a "gybe-douse", gybing the boat, not rotating the chute, and leaving it no the windward side for an immediate douse. If you are sailing a 505 worlds course, with a beat, two more reaches and a final beat after the run, you should try hard to get the spinnaker down into the port bag by approaching the leeward mark on port, or using the gybe-douse manouver. You would prefer not to have to do a windward hoist, or throw-set, on a tight reach!