Just keep a list of interested potential investors. As a founder you should be explaining the business to everyone and listening to their reactions. That means

Just keep a list of interested potential investors. As a founder you should be explaining the business to everyone and listening to their reactions. That means everyone - including other-sector people, non-tech people, your family, your friends, your neighbors, random shopkeepers, people in the lift, people in the carpark, people on the plane. If they are bored or zone out, you are doing it wrong. Improve. For ideas with strong potential and decent capital requirements, once you've got the pitch down write a decent investment prospectus document aimed at larger scale institutional investors. Find some and test their reactions. Don't spend too much of your time on the small fries. For ideas with minimal capital requirements, don't waste time raising just execute and beg/borrow/steal until you get cashflow positive.