Edit with more details:
Choosing where to go: get a big map and an imagination!
Flights: Just booked mine as I went and that seemed to work out well costwise. In any case try to overland as much as possible, it's more interesting.
Packing: Bring as little as possible, I had a 50+10L backpack and it was more than adequate. Every litre extra you pack is more and more hassle when moving.
Visas: This obv depends on where you're from and where you're headed. I sorted visas for Iran and India before leaving home (Ireland). Generally what the article says is true, it's usually possible to throw some money at the problem and get visas while on the move if necessary. Some visas run from time of entry, some from time of issuance (particularly India) - pay attention to this!