Okay
as follows in no particular order
1- V sits.
Sit on the floor, legs infront of you. Now push your body off the ground, your legs should still be on the floor. Now supporting your upperbody with your arms, raise your legs off the floor and hold them straight in front of you. Hold for 60 seconds... that is an L-sit.
Self explanatory, you look like an L floating off the ground.
A V-sit is one step further, fold your legs up to your body, and back down to L-sit.
The upper body, and hip/leg strength may be a limiting factor (some people cant get up for more than half a second at first)... but these will improve very quickly)
For v-sits, ideally you want to keep your torso perpedicular to the floor, and then bring your legs up so there perpendicular to the floor as well. but untill you gain the flexdibility you can lean back with your torso so it becomes more parallel, to help bring your legs farther up.
2. Full leg raises. As explained in V-sits, but this time you are hanging from a chin bar with your arms. You pull your legs up so they are parrallel with your torso
Alot of people lean back with their torso to get their legs perpendicular to the ground, and pretend there increasing the range of motion.
There not... there just changing the angle... which makes no diffrence
Keep your torso perpedicular at all times, and bring your legs up to your chest. dont cheat by leaning back.... this is where the flexibility comes in. but man youll notice it. I promise
3. Slide outs. Youll feel this all over at first, but it will become more of an ab exercise as your overall body strength progresses. Start in a pushup position, and slide your legs, or walk them out further behind you, untill your arms are more infront of you, than directly below you. you should start to feel the tension in your trunk muscles. keep going to a point where you can hold it for 60 seconds. try this for 3 sets. get lower each rep.
4. Reverse handstand.
Start in a handstan position, (do this against the wall if you need to) and fold your legs down to your face, keeping them straight (as you are in all the exercises listed above). If you can get them to 90 degrees. Good job. any further, and its that much better. that extra range of motion that most people cant get without the flexibility makes all the diffrence in a great six pack. actually i shouldnt say that. most guys who do these sort of movements have 8-12 packs.