Evaluate Everything
First things first, evaluate every album you get from playing through a main stage. These come in the form of upgrade parts and new weapons. When you’re at a low level, you’ll want as many weapon options as you can possibly get. Besides, if you happen to get duplicate weapons, the money you can get from selling it off will probably be higher than what you paid to evaluate it anyway.
So far, players have discovered 6 different colored albums that indicate their level of rarity: black, gold, green, blue, red, and purple. The rare albums can only be obtained through missions, though the drop rate of these seems to be somewhat random.
You’ll also be able to purchase weapons from the in-game store and sometimes the weapons being sold there will come with equipped parts. However, I’d advise against spending too much gold buying from the store; the really good stuff can only be found in chests.