A user NOW? Here's a few of my own

Don't get caught up in altcoin's claims. Seriously. Even if it's doing great, when bitcoin moves all money flows from alts back into big daddy BTC.
DO NOT be the first to send in a transaction where you're receiving a physical object. Someone shipping something has a lot more methods to get their property back than you do to get your BTC if they decide to simply not send the item.

Shop around a little with BTC. It may seem silly at first putting in the address and all, but it's actually pretty cool how much easier it is to send payments than putting in all your card info etc.