The visitors suffered a seven-wicket thrashing in the final ODI in Nagpur on Sunday to slip to third in the world rankings. They started the series in second spot.
The latest defeat was Australia 's 12th loss in their last 15 ODIs away from home -- a worrying loss of form for the team just two months ahead of a home Ashes series against England.
"We're just not taking our words out in the middle and doing it with actions. We have glimpses of it and we play well in periods and then we just get ourselves in trouble," Smith told reporters in Nagpur.
"Probably from poor decision making under pressure, that's what I probably put it down to. That's something that we need to improve on because it's not good enough."
"Probably lacking consistency with the bat I'd say ... I think we're losing wickets in clumps very consistently and that's not good enough," said Smith.
"We probably didn't adapt as well as we would have liked."
Top Australian batsmen were guilty of not converting their starts into bigger scores, costing the visitors against a formidable Indian side.
Smith's own form with the bat was not up to his usual high standards in the five matches, scoring 142 runs with two half-centuries. David Warner and Aaron Finch were the only Australian batsmen to make centuries.
"I wasn't feeling great at the start of the series to be honest. I wasn't holding the bat the way I would have liked to," said Smith.
"As the leader of the team it's been disappointing but I guess sometimes that's cricket. You have those periods where you're not getting the scores you like.
"It's something hopefully I can turn around and hopefully contribute in the T20s."
Smith played his 100th ODI in the series, having made his debut back in 2010.
Australia now head to Ranchi for the three-match Twenty20 series starting Saturday. The second and third T20s will be played on October 10 and 13 in Guwahati and Hyderabad.