This all sounds fake... but you can ironically go to gyft.com and purchase a target gift card and get your food there!

YOU DON'T EVER SELL!

Actually you sell when your profit margin is high enough that you can sell without taking out too much of your investment, which is currently potentially invaluable. Doubling your investment and cashing out what you put in while leaving the other half to simmer has always seemed like a good idea to me. If you make enough to pay off your house or car or credit card or whatever that also seems like a good idea.
It's not so much that you shouldn't cash out, but that you shouldn't cash everything out. Or that you start using Bitcoin as a commodity rather than an investment. If you're gonna have enough faith to cash in then you should have enough faith to leave some cash in.
The ultimate goal is that Bitcoin will be accepted same as cash, that's really kind of what you're investing in. If that's not what you're investing in then what are you investing in? Invest disposable cash into it, then if you want to dispose that cash cash some out, or purchase a gift card, or someday maybe a car

Spending is indeed also important! Gyft.com is a great place to trade in your Bitcoins for something of value. Besides gas and groceries and maybe a car what can you not get with an amazon gift card?

Buy and hold is the best strategy. If it "crashes" that is just an opportunity to buy cheaper.
Too many are caught up in the whole "buy" "sell" make a quick buck thing and most end up losing money "gambling" in Bitcoin. Bitcoin is meant as a means of commodity and not a way to get rich quick. While you can possibly make money this way, you are only hurting Bitcoin by selling with everyone else.
Overall Bitcoin is always rising in price and you will make money if you hold your coins. When the price goes high enough you might want to cash out some profit but don't cash out everything or you'll regret it because it's always on the rise. When the price "crashes" a couple hundred bucks the pros are laughing at you while you cash out and buy your cheap coins to hold. True believers hold strong because they know the price will correct far beyond the drop and don't panic because they have already made more than enough to compensate for the "crash".
Bitcoin is about more than making money. Although making money is nice.
Day traders are bad gamblers who generally lose money or greedy greedy people that don't care about Bitcoin as a commodity. Bitcoin is about Bitcoin, not fiat!

Just my two coins