Record workouts and weights, preferably in writing.
Try to increase weight whenever possible, but good form takes priority over weight.
Eat big, get big. Eat a lot of food, with a lot of protein, and drink your whey.
Get enough sleep, and don't drink or smoke too much.
To improve shoulder mobility, foam roll and massage your pectorals, do doorway pectoral stretches, and do shoulder dislocations with a long rod or barbell.
To improve hip mobility and posture, stretch your quads by pulling your foot behind your back, and do kneeling hip flexor stretches. Also stretch your glutes and hamstrings.
Always stretch after a workout, but never stretch right before a workout. You can hurt yourself that way. Try to stretch at least twice a day. In the morning at at night is great, and once right after a workout if it's a workout day.