in case you wanted to go to Mars

One day we'll be able to go, and once we do, you'll need to know when it's the best time to start, and what to take with you for the journey. We'll consider only economy travel, not business, first class, and not hitchiking either.

It's all about physics. We're so attracted by our planet that leaving it is just too hard. If you disagree, try to jump, and see what happens. That law of attraction is not "The Secret", but it's surely proportional to your mass (sure enough, if you eat less, you'll be able to jump higher), and to the mass of the Earth. It would be much much easier to jump up from the Moon. So, first of all, we need a kick start, and that kick start will be larger if we need to carry a lot with us. But we'll think of that later. 

The kick shall be large enough to free us from this Earth attraction and circle around it, just like the Moon does, into an orbit around the Earth. And then another kick shall move us in the direction of Mars. 

As soon as we move away from Earth in fact we'd be captured into an orbit around the Sun, this last kick would put us in a transfer orbit, called Hohman transfer, which at some point interjects the orbit of Mars. At that time we'd just need breaking a couple of times, and we'd fall into the red planet.

But leaving the Earth to go to Mars is not an everyday business. Only once every two years the planets are in such a relative orbital configuration, which allows them to meet after some time.

So, first important thing to retain: you can go to Mars only every two years.

And if you really want to save fuel, you'd take the best of the opportunities, which only happens roughly every 15 years. 

Now, assume you want to go, you'll have a couple of choices. One way to go is via a longer route, which takes 1000 days round trip. You'll have quite a journey back and forth, but you'll be able to stay on Mars for 500 days. This longer route is also the cheaper, it's using a conjunction orbit.

The other option, using an opposition orbit, is mosre costly in terms of energy (it requires a larger kick), but it's faster, it ONLY takes 500 days round trip. The problem is, you'll only have 60 days on Mars. And that's not such a long time. Plus, you'll better not forget the departure time, and keep your rocket fueled and the batterie charged, because in case you missed, you'll have to wait for another two years to come back.

The good news is, you'll have plenty of time to refuel or recharge your batteries. That is, if you took enough water and food for the extended trip ...