The Pheu Thai Party thanked voters in Sukhothai on Monday after its candidates managed to win all four constituencies in the province.
Somsak Thepsutin, a key Pheu Thai figure, said while the party won 10 constituency seats across the lower North, the number was below its target.
"We had set a higher target, but we must respect the people's mandate," he said on Monday.
From now on, he said, political parties will have to adjust the way they operate, noting parties must incorporate technology to reach out to more voters during campaigning and communicate with their supporters.
"What happened in the poll merits attention and study. It is a real eye-opener.
"We have to admit that even though Pheu Thai has good policies, the presentation of its policies was inferior to that of its rivals," Mr Somsak said.
Meanwhile, a Pheu Thai source said that the party blamed its failure to win seats in several provinces in the Northeast, such as Chaiyaphum, Nong Khai, Ubon Ratchathani, Udon Thani and Khon Kaen, on its weak election strategy.
"Moreover, some of our candidates were too complacent, thinking that the party's popularity was high, so they did not try harder to woo voters.
"In some cases, it was about putting the wrong candidates in the wrong constituencies,'' the source said, adding that the election strategy was formulated by only a small group of people within the party who were out of touch with voters.
Varawut Silpa-archa, leader of the Chartthaipattana Party, said that even though the party managed to retain its seats in all five constituencies in Suphan Buri, the party's traditional stronghold, its rival the Move Forward Party secured more party-list votes than Chartthaipattana.
Sunday's election reverted to the dual-ballot method, in which one ballot was used to select a constituency MP and the other to select a party to lead the government.
"This is a lesson that the parties could learn from," he said.
"While our candidates worked hard to meet and woo voters, they were no match for rivals who came on the back of their parties' rising popularity."
