I actually like working from coffee shops when they're busy. The more noise the easier it is for me to concentrate. But if I can easily make out several conversations, then I find it difficult not to listen and it becomes more difficult to concentrate.

Comfortable, over-the-ear headphones are always a huge plus if you enjoy listening to music while you work (beyerdynamic headphones are very nice, although a bit expensive).

Everyone is unique. I work well in both very quite, and very noisy environments, but not so well in-between. You just need to figure out what works for you.

Don't get open-ear headphones. I received some nice entry-level ones (Grado SR60), and they sound wonderful - but background noise is a problem. The coffee shop-office strategy takes some experimentation to get right.

If you want pure DB reduction, shotgun-type ear protection works but looks weird.

I find the Bose QC2/Audio-Technica ANC-7 headphones do a good job at reducing low-frequency noise disturbances (e.g. train noise) but don't really do much with random background conversation chatter.