Manage Your Energy Wisely

I had a time in my life that I was responsible for the growth of a startup in London, was giving consultancy to an eCommerce and working on my side project, all at the same time.

I knew that if I wanted to keep doing everything and not lose my sanity, I would need to manage my energy wisely.

By doing some research and experimentation, here's what worked best for me:

Eat a Breakfast Low on the Glycemic Index

What do you eat for breakfast? How does it make you feel during the day? Does it give you a boost of energy but then after a few hours you're begging for your bed?

If your energy levels start to drop at 11am, can you imagine how it will be when you arrive home at 7pm after a long day of work? How can you find energy to work on your side project in that situation?

That's why it's highly important to eat a breakfast low on the glycemic index.

 The glycemic index or glycaemic index (GI) is a number associated with a particular type of food that indicates the food's effect on a person's blood glucose (also called blood sugar) level. - Wikipedia

Low Glycemic Index foods release glucose more gradually into the bloodstream, providing you a steadier source of energy.

Think of it as like a fuel for your body. Low GI foods provides you fuel that's used gradually during the day, while high GI foods burns most of your fuel to accelerate in the beginning, and leaves you short of it during the rest of the day.  
Here are a few suggestions of low-GI foods for your breakfast:

    Eggs
    Oatmeal
    Yogurt Smoothie
    Grapefruit
    Mango
    Low Fat Cheese
    Whole Grains
    Berries
    Mushrooms
    Bananas
    Apples
    Natural Peanut Butter
    Wheat Bran Based Cereal

But especially, make sure to get the sugar out of your breakfast.

Take a Coffee Nap

If you can, taking a coffee nap of 15-20 minutes can give you a quick boost of alertness.

British researchers, Horne and Reyner, discovered that drinking coffee just before taking a power nap can be much more effective than regular naps.

Caffeine requires roughly 30 minutes to take effect, so it  kicks in just as you're waking.
Just be careful to not drift into the slow-wave sleep stage, which could give you the opposite results: grogginess and disorientation. If you sleep more than 30 minutes, you could end up in this sleep stage. So keep your nap at a maximum of 30 minutes.

Do it just once

Is there anything that you do many times a day? Answering emails or checking social media for instance?

Following the same line, is there anything that you do multiple times per week? Going to the supermarket or meetings could be that?
If yes, one good solution is to chunk your time. It will require some willpower to deal with your email just once a day, but you will get used to it eventually and also discover that people will not die if they have to wait a few hours or a day to get your response. Sometimes they will even figure out the answer themselves.

If you cook your own dinner, one good tip is to prepare food in bulk. This way you won't need to cook everyday.This tip will save you not only a lot of energy but also time that can be used on your side project.

I've learned this productivity trick. So, it's fair to give him the credit for this one.

1 hour of preparation could save you 10 hours of work

When you seat in your desk to start working on your side project you should already know exactly what you are going to do.

If you need to figure out what to do, then search for the information that you need, to then finally get started... it will require a lot more energy from you.

In some cases, you will simply skip it because you won't have enough willpower to go through all this.

What should you do to avoid it? Preparation!
 
Organize the information that you need when working on your side project so you can easily access it.

Write your to-do list early in the morning or before going to bed. Don't wait to do that when you should be working on it.

Use bucket lists. If you have one idea, don't fall into the trap that you will remember it later. Have a place where you can write it down and have easy access later. This way you won't waste your time trying to remember what was it about.

Organize your environment to help you produce your best work. Turn off your phone when you enter this environment, buy a printer if you constantly need to print stuff, leave the books that you will need to consult nearby, buy a comfortable chair and so on.

Cut down what you can survive without

That's probably the hardest part. If you want to focus on your side project, you will have to accept the idea that some things will have to change.

Have you been too social lately? Well, now you will have to become a little more anti-social.
Just go to the parties that you can't say no. Like your best friends birthday for instance. For the rest, just say politely that you are involved in a important project with a crazy deadline and that hopefully you will be able to get back to the social live soon. The last part is not true. But who cares?

Do you have many hobbies? Well, it's time to choose just one and leave the others behind for a while.

Do you like to watch TV? Sell it on Ebay.

It's time to focus. Less is more. And if you are serious about your side project, it should be in the top of your list.

Always remember what drives you

Even if you put into practice all that I've mentioned in this answer, there will still be days that you will feel tired and without energy to work on your project.

The only thing that can help you in these day is your "why".

Why are you working on this side project? What drives you to make it happen?

Write it down and read it everyday. Especially before start working. There's nothing like a good why to put you in movement.

Do not sacrifice your night of sleep

I know this was already mentioned in other answers, but I can't leave it out of my list. Because without this one, all the other tips above will have little value to you.

That said, my recommendation is: If you need 7 hours of sleep to feel rested, then don't sleep less or more than that.

A few important things to bear in mind:

Avoid bright lights late at night

Nighttime light exposure suppresses the production of melatonin, which is a hormone that your body produces to make you feel sleepy.
Watching television, checking your emails, playing games on your mobile, and all those things you love doing late at night are ruining your sleep. Avoid them at all cost.

If you have to use your computer for whatever reason, I suggest you to install Flux [6], which is a tool that adapts your screen brightness to the time of day.

Avoid "social jet lag"

If you go to bed at 10pm during the week and wake up at 6pm, and then on the weekend you go to sleep at 2am and wake up at 12pm, then your Monday will be a disaster. You will feel like you have just traveled to another completely different timezone. That's why it's called "social jet leg".

Start a sleep ritual

If you take more than 20 minutes to fall asleep, then you need to do something about it.
When you practice a night ritual constantly, your brain will start to assimilate the idea that it's time to switch off [8]. My ritual is the following: Brush my teeth, write on my journal and read a book. It doesn't need to be complex. It needs to be constant.

One last word

Don't try to do everything at once. Choose 1 or 2 of these points and try to implement them. When you start to see the results, then move to the next. It will take you some time to get there, but if that means being able to launch your side project, then I guess it's worth the effort. Isn't it?