The Welsh champions would cause a major upset if they overturned the Croatian side's 2-0 lead.
"We've got to grow into the game, not throw everything at them early on because if we concede an away goal the tie is near-enough over," said Ruscoe.
"Hopefully we can get that goal in front and put them under pressure."
Rijeka ended Dinamo Zagreb's run of 11 Croatian league titles last season.
TNS overcame Europa FC in the first round - where Rijeka had a bye - after a thrilling extra-time win against the Gibraltar champions.
Ruscoe also hopes the unfamiliar surroundings and artificial pitch will unsettle the visitors.
"We're playing on 3G as well, a small changing room at a stadium that doesn't have that atmosphere - it's all different to what they're used to," said Ruscoe.
"All these things possibly go in our favour."
Manager Scott Ruscoe hopes The New Saints can overhaul Rijeka in Tuesday's Champions League second qualifying round, second-leg tie.