One of the most important things you could do if you dont have a heavy bag yet is SHADOW BOX in front of a mirror that will help you get used to throwing punches which can be akward for someone whos never boxed, focus on proper technique and speed and also alot of short flurries this will also strenghten and conditon the ligaments and tendons in your arms and shoulders, so when you begin to hit the heavy bag you wont injure yourself..also keep moving on your toes and move around .. and for your lowerabs you could do reverse crunches , leg lifts . and hanging leg lifts...