When reciting a blessing on different foods or mitzvot one must have in mind the meaning of the words he is reciting. (Shulchan Aruch Orach Chaim 5:1)
Our Talmudic Sages explain that it is not proper to say a blessing out of habit, spouting out words hurriedly (Berachot 47, cited in Mishneh Berurah). G-d became angry regarding this matter, sending Isaiah the prophet with these words: “The L-rd said: Inasmuch as this people has drawn close, with its mouth and with its lips it has honored me, yet it has distanced its heart from Me.” (29:13)
The Piskei Teshuvot explains that when reciting a blessing one should imagine that he is standing in G-d's presence, speaking directly to Him (Avodat Yisrael). One should also say the blessing loud enough to hear his own words, since hearing the words helps one to concentrate properly. (Shnei Luchot HaBrit)
It is forbidden to pronounce G-d’s four letter name as it is spelled: yud,
vav & hei. In fact, according to the Arizal it is even forbidden to say all four letters unless one inserts another word in between them. Accordingly, G-d's four letter name is written one way, while pronounced another. The written word is spelled yud, hei,
vav & hei – but it is pronounced Adonai, meaning “my Master”. This name is usually only pronounced this way during prayer; when not praying the widespread custom is to say “Hashem”, literally: “The Name”.
When reciting G-d's name one should have in mind that the name as it is pronounced means that G-d is Master of all, and the written name means that G-d is eternal, namely that G-d was, is, and always will be. When reciting G-d's name Elohim (when not praying the custom is to say Elokim, making a “k” sound so as not to pronounce G-d's actual name), one should have in mind that G-d is powerful, all-able and the true possessor of all worldly powers (Shulchan Aruch ibid.). According to the Vilna Gaon, when reciting G-d's four letter name, halacha requires only that one have in mind that G-d is Master of all, except for the first verse of the Shema, when both explanations are required (cited in Mishneh Berurah).
One must be careful never to recite a blessing in vain, or to recite a blessing that is not necessary. If one says a blessing in vain or utters G-d's name in vain, he should immediately say: Blessed is His name, Whose glorious kingdom is forever and ever. In Hebrew: Baruch Shem Kavod Malchuto Le'olam Va'ed. (Kitzur Shulchan Aruch 6:4)