100NL at B2B.

This is a situation I often get myself in and I have big troubles with them. You get a nice hand on the flop, and are afraid of straights/flushes etc because your bets just gets called. When the scare card hits, what do you do? I know this depends, but like in this situation where reads are zero (just sat down), what is the general approach?

Sorry for the crappy HH.

MaggieD (EUR 75,35 in seat 1)
Mr_Big (EUR 69,93 in seat 2)
_Julle_ (EUR 45,10 in seat 3)
keckoo (EUR 33,15 in seat 4)
zampik (EUR 45,02 in seat 5)
tehsuk (EUR 106,30 in seat 6)

Dealer: MaggieD
Small Blind: Mr_Big (0,50)
Big Blind: _Julle_ (1,00)

tehsuk was dealt: :Jh: -:Th:

keckoo Call (1,00)
zampik Call (1,00)
tehsuk Call (1,00)
MaggieD Call (1,00)
Mr_Big Fold
_Julle_ Check

(Pot is 5.50)

Flop :Js: - :Jd: -

_Julle_ Check
keckoo Check
zampik Check
tehsuk Bet (4,00)
MaggieD Call (4,00)
_Julle_ Fold
keckoo Fold
zampik Fold

(Pot is 13.50)

Turn :Js: -:Jd: - -:Ah:

tehsuk Bet (9,00)
MaggieD Call (9,00)

River :Js: -:Jd: - - :Ah: -

tehsuk ?????

Should I even be afraid of a flush? How much do I bet? This hand confused me a little, I don't have a great jack kicker either.