Yea, trade ports and refineries are very important.
Trade ports: Build one on one side of your empire, then one on the opposite side. Any planets that are in between should be have a trade port built on them. Try to keep this line away from open fronts though, the last thing you want is other empires having a nice piracy campaign, and you can't reroute your trade ships.
Refineries: Find a planet that directly connects as many high resource 'roid to it as possible and build three refineries there. Mines can only take 3 refineries at a time and the ships will only make two phase jumps, to a bordering system and back. Try and build the most efficient (no overlap) system as possible. For example, on Systems at War (I think that's the name), its best to build 3 refiners on the asteroid planet opposite your capital and 3 on the dead-end desert world, that way nothing overlaps. As with trade ships, try and keep it away from other empires.
You will be swimming in credits, metal, and crystals in no time!