When you earn Bitcoins through tips, it is much like accepting Bitcoin as a means of payment. You need a wallet, a QR-code with your Bitcoin address on it and the people who can potentially give you a tip need to be aware of it. There are various places where you can receive Bitcoin tips.
Again, your shop is the first thing to start with in case you have one. It's just a bit simpler because since tips are voluntary you don't really need to check the incoming payment and the exact amount. Simply display the QR-code and check each day what came in.
With tips, the nice thing is that you don't necessarily need to have a shop. A blog for instance or any other website is sufficient. You can display the QR-code or just your Bitcoin address at the bottom of your page or wherever it seems convenient and let people decide how much they want to tip you. You can also view how this looks like in the footer of this German blog bitcoins21.
Another really cool way to get tipped online is ChangeTip. This service allows you to integrate tips on all major social networks, YouTube and GitHub. Very nice!
Imagine you have a restaurant and want to encourage your customers to tip with Bitcoins, there is this nice service: bctip is a website where you can print little paper vouchers that have a certain Bitcoin balance on them. When your customer has one of these, he or she can simply give it to you or your employees and you can redeem it like a coupon.
