Never sell with the purpose of "locking profits". This means that your end goal is more dollars instead of more bitcoin. You don't get it yet.
Never sell with the purpose of "buying back lower". You cannot predict the market. It is much more likely that you will do better by simply hodling long term.
Spend all of your fiat first before you even think about spending your bitcoin. Once you're out of fiat, you can spend a small percentage of your bitcoin if you need to. Spending bitcoin is the only way it can be distributed to people around the world and become universal money.
If you're an employee, increase your income by improving your skills and climbing up the ladder (either through promotions or applying for new jobs).
If you're an entrepreneur, provide as much value as you can with your product or service. The bigger the problem you solve, the more money you'll make.
Source and link to Reddit topic: This is the way: Accumulate as much bitcoin as you can, as frequently as you can, for as long as you can. Slow down a bit during bull runs when everyone is euphoric and greedy. Go harder when everyone is fearful of the price dropping further.