I won't claim to be a fitness expert, but through my personal experience, this is what I would recommend:
For the stomach, yoga + pilates do a great job at strengthening the core muscles. But if you don't like yoga/pilates, you will need to target the 6 main parts of your core muscles - upper abs, lower abs, obliques (x2), lower back muscles and the lateral muscles that hold up your core (this works like a corset that goes across your trunk). Remember not to over-work the muscles as too much will cause muscle breakdown.
Control and form are the most important - no point doing 200 lousy crunches!! Rather, do 15 - 20 for each target muscle group. Let me know if you want more info on that!
For the arms, the main areas are the biceps, triceps and the shoulder. Since you are female, I guess you won't have to worry about forearms (guys are somehow obsessed over muscular forearms). The push up is very much overlooked - it's one of the best exercises that targets so many muscle groups - biceps, triceps, chest and shoulders. Also, if you want to take a challenge, prop a Bosu ball (like a semi circle) and put your arms on it instead of the floor - this will also work your core like crazy. Go slow at first and don't over-exert - start with your knees on the floor and then gradually build up the intensity by going on the toes, and then on a flat bench, if you're up for a challenge!
A lot of ladies I know also do simple arm exercises like dumbbell bicep curls (keep your elbows by your side at all times and do NOT swing your body and use momentum!), dumbbell kickbacks (for the triceps. very effective for toning the little buggers!), side dumbbell raises (you stand straight with dumbbells in your hands, and lift it 90 degrees to the sides. Remember not to 'lock' your elbows as it might be too pressurising on the joint.
Legs-wise, you will want to do loads of body-weight squats (form is vital: don't let your knees go past your toes as it'll damage your knees!), lunges (90 degrees on both legs when you sink down), leg raises (lie down on your side and lift the upper leg up to 45 degrees). And if you join a gym with exercise classes, join the spinning class - it'll smash your legs and make them toned!!
All the best for achieving your goal!!
Let me know if you want/need any more information! Sorry for the lengthy post!!
I work my obliques and back muscles one day, and my upper and lower abs another. 
