The first requirement would be… A body!
Then, determination – a super power that manipulates time (Really. Only through determination and a bit of scheduling, you then can find time for yourself.)
An empty notebook to record all your workouts, track your progress. Not an option. You will thank me.

One of the good thing about cross train is you don’t necessarily need to join a gym. A gym would help, but basic fitness can be achieved with a series of body weight training.

All you need is about 20 minutes a day, up to an hour, FULLY FOC– USED.
For newbies, all you need to do is practice one basic moves in these 20 minutes, everyday.

Strict Pushups – Chest and triceps, and a bit of abs. Hundredpushups.com is a site gives a very good guide for you first 100 pushups a day. Make sure your chest touches the floor and arms straight when you are up. No short cuts. You will need a strong base when you start doing diamond pushups, wide pushups, military pushups, hindu pushups, balance pushups and more.

Pullups – Back, biceps and grip. Helps straighten spine too. Do it at the local playground. Try assisted pullups when you just started or when crunching for last few reps.

Squats – Some said this is mother of all workouts. Strengthen knees and glutes, which you will need them for running and jumping, and when you are 60.

Lunges – Like squats, but works the same muscle differently.

Box jumps – Calf and ankle. Builds explosiveness. Start with something like 12″, then move higher as you progress.

Breathing – This might sound cliche but it is important to get enough oxygen into your bloodstream between sets or during HIIT. Some workouts requires belly breathing while in mobile, such as running, and others requires you to hold your breath, such as weighted squats.

Stretching – Prevents injury, increase rate of recovery, flexibility and blood flow. Need I say more?

Running – Cross train doesn’t neglect cardio. There are tons of training method. Explore all of them.

Warmups – Starjumps, light jog, whatever. Everyone has a set of warmup at different stage of fitness level. Explore what makes you hot.

Burpees – Pushups and jump. Chest, tricep and legs. You may do 100 to gauge your fitness level once in awhile.

Rope jumps – Calf, ankle and cardio.

Swimming – overall body and cardio.

There are no short of things to do when comes to cross training. When you got these basics right, venture into combination of above mentioned workouts. Start small, something like 5 pullups, 10 pushups and 20 squats, AMRAP (As Many Rounds As Possible) in 20 minutes. Push hard only when you feel like you can do more.
Like 10 pullups, 20 pushups and 30 box jumps, 20 minutes AMRAP
Or 400m run, 10 pullups, 20 pushups, 20 minutes AMRAP

Time your workout, focus, breathe, and challenge your previous record by doing more, or faster.
Happy exploring!