If someone plays a strange move in the opening do the following:
1. Think! Don't blindly carry on with a "book" move - it might not work now that they have deviated from the line you are familiar with.
2. Look at what they might be trying to do with their move. Make sure that you are not going to overlook a threat.
3. Look at what they have weakened (if anything) by playing such a move. Depending on the move it may require that you change your strategy or just carry on as normal.
4. Remember basic opening principals. If you are in doubt developing quickly is usually a good option.
5. Don't necessarily try to "punish" their move. If you see a good tactical response then go ahead but remember that sometimes their move isn't book because it simply isn't the best move available. For example if white starts with 1. a3 then there is no way of punishing that move. However other moves such as e4 and d4 are preferred because they are considered better. Black should just continue as normal and look forward to a good game.
Basically, don't remember variations, remember principals :)
Hope this helps!
Let me explain. I´m fairly new to chess, so I´m fairly new to the opening I play for White, The Scotch. I pretty much have the book moves down up to move 10, but how many opponents play by the book, lol. This weekend for example, while playing the Scotch, I saw d5, d6, and f6 on move 3 for Black. None of them main line. After these games I compare the pgn file to a data base to see what were the best possible moves I could have made as White. Now my question to you more experienced members here is the following, what is a good way to keep track of these variations so that I know how to play them when they come up again? I have a good memory, but not good enough that going through the lines once with the data base I can remember them. I could write them down in a note book, but I am much better learning something visually then just looking at the games notation. Whenever I follow someone´s notated game, I need to set up a board or use the PC to be able to follow along. I can´t follow the whole game in my head yet. A lot of people here post their games in a thread where you can click on the buttons and scroll through the game in a kind of viewer. Something like that would be great for me, but I don´t know if it´s a program specific to this site, or one can create these files on their own computer and play through them whenever they want. I´d really appreciate any suggestions on how I can organize these non-main line variations so that I can have them ready for review when ever I want, which should be often, lol. Thanks in advance, H.G.