Ok, first of all if you just started lifting you need the basic exercises just like everyone else. I suggest that most of the time you lift with a basic program, Chris Shugart has the Dawg School for beginners articles which are really good.
Second, don’t worry about being tight from lifting as long as you stretch thoroughly and continue to incorporate plyometrics like heavy bag work and focus mitt drills into your training. Two areas to watch are your chest and triceps. Don’t do a great deal of exercises to widen your chest, that pushes your elbows out in the guards up position and exposes your chin, liver and rib cage. Stretch your triceps to make sure you can always get your hand back to guard your jaw from hooks and other curved line punches.
Third, boxing specific weight training is best done after you’ve built a solid base like I mentioned above and should be a part of your pre fight training. In general I say lift for muscle size and a strength base first, muscular endurance next, then as the fight gets closer, switch to low reps for coordination and to make sure you have the energy to do your boxing training.
Boxing requires explosive calves, quads, hip flexors(mobility and punching power), strong, well muscled abdominals(padding from impact), explosive obliques(punching power on curved line shots), traps, rhomboids, delts(these control your ability to keep your hands in front of your face and along with your upper pecs help protect your collar bone from being damaged by an overhand punch ). As far as your pecs, I’d say concentrate mostly on incline chest work because if thrown correctly your straight line punches actually go up at a slight angle to help protect your chin and your benches will build your strength at that angle. Also a deep chest will help provide a shield for your solar plexus so it’s harder to get the wind knocked out of you. Your lower back needs to be strong because all of the clinching, slipping and squatting to throw hooks and upper cuts takes a toll. Build your forearms with hammer curls, reverse curls, because that also increases your punching power and keeps you from hurting your hand.
Definitely do bridges because you need a strong neck to help avoid getting knocked out or whiplash from a strong curved line punch(like an overhand right or hook).
Finally, if the moderator wil permit me to mention a website, Ringside publishes a weight training manual for boxers. Just go to their website and request a free catalog.
Good luck and guard your grille.