Anything that increases your heart rate would be good .. running, swimming, etc. Situps are cool, will get you a 6-pack and helps with general fitness level. Pushup are only really increases arm strength, useful if you have an old shocker
.. but strong arms is useful off-field , e.g. carrying paint boxes
.
I good idea is to make yourself a training scheme, not use some elses. The way to do it is, chose the exercises that you want to do, and do as many as you feel comfortable with, stopping when you:
a) are short-breathed / can't wistle
or
b) your muscles begin to tire. Mark down how many you did
Do this for each exercise leaving time between each for your heart rate to return to normal and have a drink (don't get dehydraited).
Once you have done this and you feel comfortable with the numbers stick to them .. do them 2/3 times 2 weeks, no more. Then re-test how many you can do.
The best exercise is swimming, it uses all muscle groups and increases your heart rate while swimming. This is best done in laps of the pool, no just messing around. Though just being in water is exercising .. as your body resists the water pressure.
Anyway, that's enough from me