שַׁבְּחוּ קֳדָמוֹי זַמַרוּ קֳדָמוּ מַלִילוּ כֻלְהוֹן פְּרִשְׁוָתֵיהּ.
1. make music | זַמְּרוּ – See Radak that "לשיר" refers to singing by mouth, while "לזמר" refers to making music with an instrument. Cf. Malbim (Tehillim 27:6) that both verbs might refer to vocal expression, but that "לזמר" is a stronger verb, used exclusively in the context of singing praises to Hashem. He might translate it as: "hymn".
2. talk | שִׂיחוּ – See Ibn Ezra that David is saying that in addition to directing their song and praise to Hashem, the people should also speak one to another about Hashem's wonders. The exact connotation of the root "שיח" is debated. It might refer to talking continuously (Metzudat David), speaking in a soft voice (Hoil Moshe Tehillim 105:2), or to natural, spontaneous conversing, which is not particularly thought-out, but something habitual (Malbim Tehillim 145:5).