Here is my preferred build order, regardless of faction. I do believe it is the most efficient build order at the moment. Each line shows a number of actions that can be done all at once, the order you perform the actions on each line doesn't really matter as long as you do them all as quickly as possible.
1. Build capital ship factory / Buy 100 crystal / Upgrade home planet population / Build crystal extrator / Build scouts (Usually 3)
2. Build 2 metal extractors / Build capital ship / Build colony ship (If not building the colony capital ship)
3. Scuttle capital ship factory / Build light frigates or reserach stations (Depending on early game strategy)
From then on it depends on a lot of factors including the type and size of map, opponents and neighboring planets.