by Bankler
The 20% rule is a bit low, IMO.My rule (for a ~60 card deck) is 20% + 1 FS site (so 13/60). And one non-FS site that generates power (these are good to ramp if you get a good start). And then ~3-4 alternate power generation. My mix of FS sites varies based on the deck, but in a random deck I'll likely have 2-3 sites that can generate additional power (Gambling House, Mahjonng Parlor, Disco, Monkey House, Mobius Garden, etc).
As mentioned, Dragon's way is Dirk Wisely's Gambit. But you can also use Dark's Soft Whisper. Most factions have a card or two that can generate power, but that depends on the sets you have. The event that generates a point or two is often worth it.