A few years ago, I wrote an article listing 125 things I had learned while working in game development. It's been a few years, so I learned a lot more. Some of these things might contradict earlier points I've made, but the industry changes fast.
That also brings me to my first point:
1) Advice from over a year ago is most likely outdated now.
2) Failure might very well be beyond your control.
3) A great game might still not have a market, despite all the awards you're winning.
4) You always fail because of choices you made, if it wasn't there would be no reason to try again.
5) The indie market is over-saturated, there is no going around that.
6) If you want to make money as an Indie, do your market research.
7) Listen to the feedback (at least) that you get during development.
8) There is always a chance that you'll be successful.
9) Don't break your bank to make games.
10) Never dismiss a publisher as an option if you need financial or marketing help.
11) Don't expect miracles from a publisher.
12) If you fail to meet your release-date, you either did unnecessary work or you made a mistake in planning.
13) Don't bet on one market/platform if you want to be sustainable as a business.
14) Past achievements are no longer a guarantee for the future.
15) Coverage by media/influencers does not always convert to sales.
16) Pricing your game right is more important than ever.
17) Be creative in your marketing.
18) What works for one game, might not work for yours.
19) You're not owed help by others, because they're successful and have money.
20) You're not owed success ever.
21) Take enough breaks.
22) Listen to people with more experience, but don't follow blindly.
23) Test your game with players during development as much as possible.
24) Make lots of friends in the industry. It gives you a motivational boost and you never know who can help you when needed.
25) Seek support from family and friends when needed.
26) Talk about your game with joy and enthusiasm, never negatively.
27) Don't copy game mechanics, but do take inspiration from them.
28) Every game idea has been thought of before, don't be afraid that your game is unoriginal.
29) Learn to pitch your game.
30) Rehearse your game pitch regularly.
31) Never assume you know more then the person you're talking to.
32) Help others when they ask for your help (when reasonable), you'd also like to be helped when needed in return.
33) Share the work of others, but only if you actually belief their work is good.
34) Be honest when giving feedback to others, even when it might not be what they want to hear.
35) But be kind and constructive in the way you provide that feedback.
36) If your game offends someone, always try to rectify or at least address it. Gaming should be enjoyable and if your game isn't it not only hurts someone else, it also hurts you as a creator.
37) Use social media to promote your game.
38) Principles are nice, but they might get in the way of your game being successful.
39) But never do something you can't life with.
40) Never underestimate what audio can do for your game.
41) Never add something to your game as an after thought.
42) People will write negative stuff about your game, this will hurt.
43) Never defend yourself against negative critique (when it's about your game). You can't win this.
44) Instead address all points if critique in your game after release as much as possible and tell people you've heard them.
45) Don't use social media when under the influence.
46) Don't dismiss localization of your game as an option.
47) It will never and should never be easy to make a game.
48) Some days will suck, but the end product will be worth it.
49) Remember that your game can still be great, even when it doesn't sell.
50) Appreciate the compliments and positive reviews you get as much as the negative reviews.
If you want to contact me for questions or just a chat. Hit me up on twitter (@Ithunn) or send me an e-mail to honders.sa[at]gmail[dot]com