My 'method' is to only buy at low prices, so I wouldn't be in a trade such as your last example as the risk/reward is not adequate.
I like to trade the reversals, eg FTSE gaps up at open, I then buy a FTSE down @ a low price hoping to pick up a few points on the reversal (if there is one of course

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I'm ready for all the negative comments about 'guessing', but basically I predict where I think the market will go. For example, this morning I expected the markets to be fairly weak so I bought a 'FTSE down >30 at 12pm' at around 7:15AM @ a price of 10.7, hoping that even if it doesn't fall by over 30 it will come near to it hence giving me a few points at least. Risking just 11.7*stake with a real possibility in my view that the FTSE would fall.
I let it run and at 11:30 I closed at 78.2 when the FTSE was sitting at around -30. Nice profit of 66.5 points. I could have let it go till close and would have got 88.3 points but prices can be very volatile close to expiry and as FTSE was hovering around the -30 mark it could have gone either way. +66.5 is better than -11.7!
All I look at is price action over the current and past days and get a 'feeling' for the market.
I don't have a system as such, but look for good prices being offered on markets which have a reasonable chance of happening or getting close to happen. Buying at 10 to 20 gives good room for a few points gain as binary prices can be very volatile, moving 20+ points with just a few points move on the index itself.