Lastly, trim for power when you come out of the tack. Think of it in terms of gears. If the boat is slow accelerating after a tack, try powering up the sails immediately after the tack. Ease the backstay, foot off a little to power up, then slowly bring it back up to your ideal pointing angle....
Some good suggestions here. I just wanted to elaborate a bit more on the comment above.
There are really two issues here: Losing speed during the tack, and accelerating after coming out of it. You want to minimize the first, and maximize the second.
After coming out of the turn, there is a tendency to over trim the sails by resetting them where they were on the previous tack. But on the previous tack, the sails were released when the boat was at full speed and closest angle of attack to the wind. After coming out of the turn, the boat is at neither of these initially.
After the tack, the boat is usually sailed "fat", i.e. with sheets slightly eased and not extremely close to the wind. This allows the boat to build speed and develop lift in the foils (sails and keel). As speed increases and the foils begin to generate more lift, the apparent wind both increases and moves forward. As this happens, the boat can be steered progressively higher into the wind, and the trim of the sails must be adjusted accordingly.
It's a gradual process, lasting varying amounts of time depending on the type of boat. Ideally, the sail trimmers will gradually bring the sails in to close-hauled, with the trim corresponding closely to the boat's increase in speed and higher point of sail. Eventually the boat returns to full speed and closest angle of attack, the trimmers can go hike out, and then it's up to the helmsman to steer the tell tales.
On the other hand, if you just pull the sails in tight and try to steer closest angle of attack immediately after the tack, the boat will feel anemic and will take much longer to build speed and harden up on the wind.