Never chase up the latest shining new toons unless you are a whale.
Never unlock a toon or ship unless you are willing to invest in them fully. Especially unlock ships can be very expensive (massive GP increase).
Never apply Zeta to any toons without proper research. Some zetas are useless or only marginally improve the viability of the toon.
Focus on one good team at a time. Never build up a single toon without a full team. This is a 3v3 and 5v5 game.
Never try to build a team, which only has a niche use (a toon/team shall shine at least in 2-3 different game modes).