Here's another couple of tips you won't find in the Operators Handbook or the Flight Manual.
The gear warning horn is ONLY activated if the flap switch is either in the UP or DOWN position.
If you lower flap and then return the switch to neutral, the gear warning horn is inhibited.
Secondly, ensure that when you lower the gear, you push the Gear switch ALL the way to the bottom.
If there is any stretch in the cable that goes to the hydraulic selector, failure to do so will result in the gear doors opening giving you all the indications that it's all happening and then they'll close up again without the gear coming down.
Thirdly, check to see what MP the gear warning horn comes on (assuming the flap switch is in the down detent) as many operators set the alarm point at 12" MP.
If you're flying the engines properly, you won't see 12"MP until the flare.
Hard experience taught me those things.
