Check your base to see what kind of passengers it attracts. There will be a pie chart showing passenger destinations either domestic/international/intl lh. If you only have domestic showing 100% then there's no point looking at destinations outwith your country so that should save a bit of time. If you have International or intl lh showing and this is the type of route you are looking for think of connections between places (eg same language or historical links (eg - colonies)) as they often have high demand - eg Amsterdam to South Africa, England to USA, France to North Africa or Spain to South America. Just a couple of quick tips but hope they save you some time.