Jonathan wanted to have something on this session thinking about the English Opening, but, in case you don't play that system, I'll broaden it out a bit.

The experience of meeting novelty

It needn't be a completely new move, of course, just new to you. Let's see if we can create that experience for you. Some examples that we came up with: As White, facing 1.d4 e5!? As White, facing 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4!? As Black, facing 1.e4 e5 2.Bc4 Nf6 3.d4!? Some examples for more experienced players, can be found in the SOS volumes.  For example, here are the suggestions from SOS 13: Responses to novelty Emotional responses: suspicion, derision, fear, panic, amusement, complacency, offence, dismissal, distraction... "He must be a duffer"/"He must have studied it and know everything"... "I'd hate to lose quickly, what's the safest move here?" "What are they up to?" You have to get past those emotional responses as fast as you can and start thinking about the position in front of you right now.  The one strand that is very relevant is that last one: What are they up to?  That's always a good chess question, because your opponent is always up to something! So, looking for rational responses: it's just another move.  What's the idea? -- or, more likely, the ideas?  What are your ideas?  What moves are at all plausible for me?  What moves do I want to play anyway? Maybe there is a combative line that is quite theoretical and leads to a clear advantage for your side.  But can you find it while steering clear of any traps? Perhaps more practical is to seek a smaller, safer advantage. Let's have a look at these approaches in our examples:

Example 1

1.d4 e5!?

This sprightly idea is called the Englund Gambit.  Imagine you are facing this move in the first round of the Bristol Rapidplay against an unknown opponent.

I think it's clear that after 2.c3 or 2.d5 Bc5 White has abandoned any hope of an opening advantage.  Really the only way forward is to take it

2.dxe5

No qualms here yet I think.

2...Nc6 3.Nf3

Also qualm-free.  A very natural move, one we probably want to play anyway, and one that defends the pawn.

[3.f4 looks like Trying Too Hard.  Maybe it's good, but with 3.Nf3 available and the clock going, why bother?]

3...Qe7

OK, that is an awkward-looking move.  That may mean that Black really is a bit of a duffer, or this is an unusual move with a point.  One very natural response is:

4.Bf4

But remembering last week (loose piece, exposed King, look at all checks and captures every move) you should instantly spot the point:

4...Qb4+

Now one line that you might be tempted by is 5.Bd2 Qxb2 6.Bc3 (an unnatural move I think, and a Warning Sign) 6...Bb4 7.Qd2 Bxc3 8.Qxc3 Qc1 'mate!

That's not forced of course.  Perhaps White can improve without spending too much thinking time with 6.Nc3 e.g. 6...Bb4 7.Rb1 Qa3 8.Nd5...

However, if your analysis skills aren't up to all that in rapidplay, I think you should take one look at 4.Bf4, spot 4...Qb4+, and move on to the next most natural move:

4.Nc3

Must be OK.  Let Black have the pawn back, we'll carry on playing good strong sensible moves.

4...Nxe5

Now, Black still has some problems due to the awkward ...Qe7.  It's not hard to recommend here:

5.e4

White has easy development and a small advantage.  We can look forward to continuing our sensible opening play, perhaps arriving at a position where we have completed development in good order when Black is still trying to get sorted out, and we can then look for a way of seizing the initiative or forcing a weakness.  Perhaps 4.Bf4 leads to a bigger advantage with best play on both sides, but 4.Nc3 and 5.e4 is easier to handle and free from risk.

[5.Nxe5 Qxe5 just solves Black's problem for them: the Bf8 can now be developed.]

Example 2

As White, facing 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4!?

Again there is a fiendish trap: 4.Nxe5 Qg5 5.Nxf7 Qxg2 6.Rf1 Qxe4+ 7.Be2 Nf3# (Blackburne's Shilling Gambit)

But I'm sure you can spot the suspicious time-wasting by the White Knight.  I think a better move is easy to find:

4.c3! and now after 4...Nxf3+ 5.Qxf3 White has an obvious plus.

Example 3

As Black, facing 1.e4 e5 2.Bc4 Nf6 3.d4!?

The idea is to play the Urusoff gambit: 3...exd4 4.Nf3 Nxe4 5.Qxd4, when White plans Nc3 Bg5 O-O-O and Rhe1. I think 3...exd4 is a move you want to play anyway, but after 4.Nf3 we can find something else. 4...Nc6! transposes into the main lines of the Two Knights' Defence, which gets us back into what we know.  What's that? Oh, dear... It turns out not too many of us know the main lines of the Two Knights' Defence, but we do know the Giuoco Piano. In that case, I think we have no business playing 2...Nf6, and instead, 2...Nc6 is the only way to preserve any hope of getting into known lines.  But if White wanted to play the Giuoco Piano I assume they would have gone for it straight away, so we still need to know another line here (Vienna Game?).  At least after 2...Nc6 there will be no Urusoff. So, the advice when faced with a novel move is:

• Don't Panic, and Don't Sneer
• Ask yourself, what is the idea?
• Play natural moves, and moves you want to play anyway, when you can
• Be suspicious of moves that disobey standard opening guidelines.

"This reminds me of a rule I know very well because I made it up: When you are caught in an opening you don't know, make good developing moves!" -- Bent Larsen in Evans et al.

P.S. GM example appended