Goldfish - Don't ram unless you know what you're doing. Don't GET rammed, at all costs. Use the balloon to block incoming explosives if you don't have another option. Timing is everything on a hwachafish, time the reloads and prioritize targets based on threat level to your ally. Don't fight a pyra head on if you can help it. REMEMBER you have side guns, use them. The bifecta point for a few weapons are on the "x" that the ropes make when on the wheel and looking to the right. Keep a spanner handy to help with balloon repairs. Always look to be around your ally, the Goldfish does it's job best when it's assisting, rather than killing. If your front gun goes down, immediately look for ways to stall until an ally comes to help. Good ways of stalling with the goldie are to balloon block, or to play bullfighter, hold "descend" for a bit then hydro upwards.
I usually play more defensive rather than aggressive with the goldie so this isn't set in stone, but I would recommend a defensive gun in the port slot, namely the mine launcher. laying mines on an approaching enemy can really pay off, and if you're in the middle of nowhere they make for decent makeshift cover. If anything they will buy you a few seconds to re-evaluate a sticky situation.
The most important tip I can think of is that the Goldfish at it's core is a support ship, always try to decide what is best for your ALLY, not you. Skrimskraw put it best when he said the goldfish "Isn't about quick kills, it's about efficient kills."