"None should stand up to pray save in sober mood; the pious men of old used to wait an hour before they said their prayer, that they might direct their heart toward God." ~~ Berakhot 5:1
"One should not pray in levity and jest, but in gravity and the joy of doing good." ~~ Talmud, Berakhot
"Better prayer without synagogue than synagogue without prayer." ~~ Abraham Heschel
"The gates of prayer are never closed. " ~~ Deuteronomy (Devarim) R.
"What is our prayer for rain? “We thank You for each drop that You have let fall.”" ~~ Talmud, Berakhot
"Prayer or benediction without intention is like body without soul." ~~ Tanya
"In Ne”ilah [the closing prayer] of Yom Kippur, what did he [the Cohen] say? “And Hashem will bless you from Zion and you will see the good of Jerusalem all of the days of your life.” " ~~ Talmud, Sotah 40a
"Prayer is greater than sacrifices." ~~ Talmud, Berakhot
"Prayer is the service of the heart." ~~ Talmud, Ta’anit
"Prayer without intention is like a body without a soul." ~~ Yeshu’ot Meshicho
"Who prays in Jerusalem is as one praying before the Throne of Glory, for the Gate of Heaven is there." ~~ Pirke Derabbi Eliezer
"Eating is the best of prayers." ~~ Avrunin