As you approach the leeward mark, you want to focus on rounding efficiently, and then executing your strategy for the beat. Discuss the beat with your partner before rounding. Then round.
Take turns looking upwind. If the crew is holding the jib to leeward, it will be hard for them to look, in which case the skipper should look. If the crew is holding the jib to weather for wing on wing, then the crew will have a good view upwind. Discuss what you see and what you are experiencing. As it relates to the direction the wind is coming from, are you currently sailing in a left shift, or a right shift? Do you see any flags to windward, or boats sailing upwind to windward, that indicate the shift? Is there more current on one side of the course or the other? Are there more waves on one side of the course or other? Are there boats rounding directly in front of you? Based on your answers to these questions you will either round and continue sailing on port tack, or round and tack onto starboard tack.
With a plan formulated, begin your rounding. In this scenario the boat is sailing down wind on port tack. While sailing down wind some skippers switch to holding the mainsheet above the ratchet block. If you do this, then remember to take hold of the mainsheet below the ratchet block as you normally do for upwind sailing. Trim the slack out of the mainsheet. If the crew is to leeward, then stay there. If the crew is winging the jib to windward, then be prepared to cross to leeward on your skipper's direction so that your body weight initiates the turn more so than the rudder. The skipper should also stand up, getting their weight off the rail, to help the boat heel more to leeward.
As the boat rounds up, the skipper trims the mainsail aggressively while standing. The left hand (forward hand) pulls in the mainsheet by grabbing at the ratchet block, and then extending the left hand all the way over head. Then, with the tiller hand, the skipper uses the forefinger and middle finger to grip the mainsheet to keep it trimmed. Once gripped, the skipper reaches down again with the forward hand (left hand), grabs below the ratchet block and trims again. Because the boat is turning there should be little to no resistance while trimming. You are simply taking the slack out of the sail while the boat heads up.
Meanwhile, the crew should be trimming the jib slowly. Keep the forward six inches of the jib luffing as the boat rounds up. This way the bow can turn to windward without the jib fighting it. Once the skipper is on course, trim the jib to full trim. The crew sits where appropriate for the wind conditions, always aiming for about 5-10 degrees of leeward heel while sailing upwind. The skipper sits to windward and forward (even with the mainsheet block).