For your first start, aim to start on starboard tack aiming for about 3/4 of the way down the line. This isn't the best position as one end or the other will be better but it means you approach the line with right of way (starboard tack) hopefully in a less crowded part of the line. The start may look intimidating, but just keep a sharp lookout, apply the priority rules and be prepared to react quickly. If you take this route you just have to lookout for boats coming up to the line from your leeward (left if you are on starboard tack) side. It won't be long before you are mixing it with the rest of them. Do make sure you get to the line on the gun, don't be line shy or you will start behind everone and with their sails blocking your wind.
If it's a phased start and you aren't in the first group, please keep the line clear for those who are. Once your two-minute signal has gone, you can get into position for your start.
Then just sail the best you can; feel free to assert your rights but NEVER to the point of a collision; the rules place an onus on all boats to avoid collision if at all possible. If you pass a boat closely to windward you may well get luffed, so give plenty of room and/or be prepared to tack away. He has to give you a chance to keep clear under the new rules.
Someone on starboard tack may call 'hold your course' which means that he is happy to avoid you. He's probably doing this for some fiendish tactical reason; you can tack if you want to, just as long as you give him room. 'Hold your course' is also used by someone on port tack to advise that he's seen you and will avoid you. In class races, don't make life unnecessarily difficult for boats in another class as you aren't really racing them; defend your own position by all means, but if you are having one of those days don't wreck a battle at the front of another fleet.
The standard at IBRSC is pretty high and you really needn't worry about getting in the way of the leaders, they'll be off to the horizon. Don't worry about counting laps, just concentrate on following the correct course and keep going until you pass the committe baot and hear a single sound from the hooter. You have then finished - give 'em a wave!
If you are sure you have finished, but you didn't hear a hoot, this means that you have either missed a mark or were over the line at the start and didn't come back. Either way, your result doesn't count, sorry.
Important - don't cross the finish line again on your way back to your pontoon, this will get you disqualified. This rule is to keep the finish line clear for those still racing. On your way back, keep clear of those still locked in combat.