What I like to do when I am learning a new opening, I play alot of 5 minute games and after every game I have the repetoire book in front of me so I can reference it immediately after. My white reptoire book is Gambiteer I by Nigel Davies and Mayhem in the Morra by Marc Esserman. As black I use the The New Sicilian Dragon by Simon Williams and Grand Master Repertoire 12: Modern Benoni by Marian Petrov and Ari Ziegler's dvd on the Benoni.
New opening rep.
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For me when I want to learn a new opening I go over thousands of master games of every variation of that opening until I have it memorized. I will sometimes spend up to 4-5 hours a day going over master games of a certain opening and all its variations. If you do that you will be prepared for whatever your opponents try.
Well Rybkat, not everyone has the time to spend 5 hours a day studying master games 
I usually proceed like this, when I want to learn a specific opening:
1. Choose which line I want to play: For this purpose I usually just quickly click through some games in a database and check if I like the type of position that arises most often. This depends on whether you like open or closed, tactical or strategical games etc. and choose accordingly. You have to be comfortable with most positions you get.
2. When I have a rough idea what to aim for, I look a little closer at concrete moves and try to get the idea behind the moves that are played from you but also from your opponent. This helps a lot, if an opponent deviates from your lines, you know better what to look for to exploit a possible mistake.
3. I plug the specific opening tree into a database and learn it by heart using "Opening Training" with the "Learn Moves" feature enabled.
Nicholas_Shannon80 wrote:
Another analogy is if I was trying to write left-handed.
I just started feeling comfortable with all the e4 stuff, now I play d4
Nicholas, that is a prescient analogy. 1 d4 is often referred to as opening left-handed because it is to the left (whereas 1 e4 is to the right).
#sinister
I'm trying to learn a whole new set of openings. I've been playing them and I feel like I'm just playing drunk. It's so weird blitzing and not feeling comfortable in your prep. Another analogy is if I was trying to write left-handed.
I just started feeling comfortable with all the e4 stuff, now I play d4 and I'm trying to remember how ppl played against me when I played the Benoni, the Benko, the Dutch, the Slav, the etc. etc... Lol all the set ups they used so brilliantly against me just fall apart when I use them now. It's got me really flabbergasted!