Only regret I have was not pushing the missus into keeping our first place and renting it out. She didn't want to have 2 mortgages and so we sold it (1 bed terrace with no garden in Surrey) for £55K. The same houses now sell for nearly £200K and rent for £850-900 a month!
Anyhoo, we've played the market reasonably cannily since then and now live in a huge gaff with a tiny mortgage. We more than doubled our money on the last house we bought before the current one.