I also play Stars 25NL 6max, I play semi-loose and passive and have been overall winning (+8 PTBB/100 hands) for a month.

I would go as far as saying that aggression and c-betting are overrated at this level. People will too often call you down with anything. No one folds overpairs (let alone TP), and people will call your c-bets with anything, from a missed small PP to a gutshot to overcards. Which means you sometimes have to fire multiple bullets (which could be scary).

Last night I tried playing more TAG (I ran at 24/15 while my usual numbers are 29/10) and I lost 6 buyins over 1k hands. I almost always raised with PPs and good suited connectors 1st in, c-bet in position, and found people calling 3 barrel half-pot bluffs with bottom pair while I missed my draws.

Keys to succeeding at this level (IMO):

Get good cards (i.e. flop sets get paid)
Identify the regulars and avoid them
When you play draws go for implied odds rather than fold equity.
Get into the pot cheap (i.e. limp / call moderate raises with suited gappers / suited aces / PPs in all positions, and let go if you don't hit!)
Read your opponents (this is definitely achievable)
Attempt to trap only against aggressive competition (e.g. limp-call PFR with AA/KK)