I would like to know what is the best way to tone up my buttocks? I am approaching thirty and am worried about everything getting saggy.
Barbell squats and barbell deadlifts are both excellent movements for your glutes/lower body.
EDIT - It has been requested that I elaborate on how to perform these movements, which is a bit daunting considering there have been entire books devoted to how to squat and deadlift, but I'll try to give a concise rundown:
These are the cues I think about to keep my form as good as possible while doing these movements. Please comment if you have other helpful cues.
I agree with BenWillkommen's suggestions.
I have two more which don't require a gym with a squat rack...
Legs=any part of legs really. Cardio helps because it trims fat and tightens everything, so I would suggest that as well. Specific to quick easy leg exercises that aren't mentioned above, I would do any of these things:
Air squats, forward and side lunges, sprawl, wall chair, and lots and lots of jump rope. (if possible)
Vary it between lots of fast reps and holding in place for 30+ seconds or however long you can stand it.
DO them CORRECTLY and form first, reps second. You'll majorly mess up knees and back if you do them with bad form.
Someone asked a similar question here that I answered: Quick leg workout without equipment
Just something different, I think you will like these 2 exercises, frog jumps and platypus *walk* from celebrity trainer David Kirsch. See this video of Victoria Secret models tryout/contest:
A. Grasp a medicine ball with both hands and extend your arms overhead. Squat in a sitting position with your knees aligned with your toes and your butt sticking back as far as you can get it.
B. Keep your core tight as you walk forward, pushing off through each heel. If you perform the move correctly, your butt and inner thighs will be on fire. Walk across the room in one direction and then reverse and walk backward. If your room is small, repeat crossing the room one time before moving on to jumping lunges.
A. Squat down while sticking your butt out. Keep your knees just above not in front of your toes.
B. Spring up while thrusting your arms overhead. Land on your heels, rolling forward onto your toes.
There are tons of butt toning workout from David, as he's clients are mostly women, I think you'll like his exercises. Hope this helps
I agree with @Ben's answer as far as squats, deadlifts and lunges being good glute exercises. Additionally, you may want to check into Callanetics. It is based on short, repetitive movements at the end of the range. This approach specifically targets the deep gluteal and hip muscles that help to contract and lift the buttocks. I'm sorry I can't find a link to a picture that shows the progression of the buttock line lifting.
Another similar program using these small isometric type contractions is Pure Barre.
Given your goal of tightening up and lifting the buttocks, I think you will be happy with these types of exercises. Just realize that these exercises only deal with shrinking the space you occupy. If you need to lose weight as well, follow good diet principles and appropriate calorie burning exercises like HIIT.