Don't keep things to yourself, if you have a business idea talk about it. Many people feel valued for being asked for an opinion furthermore they may enhance or inspire the idea put to them. Talk to your partner, even talk to yourself that may sound crazy but sometimes it really does help.
An idea always looks different if from looking at it from your own point of view which is why it is so valuable to get a different angle from others. They will spot flaws that you may well have not noticed. From that point alone it will save you time and effort realising this for yourself later down the line.
Never forget, it's free to talk which means free advice.