Ashrei is recited before the Amida during the Minha service, marking the third time that we recite Ashrei over the course of the day. This practice is based upon the Talmud's comment in Masechet Berachot that whoever recites Ashrei three times each day – with concentration – is guaranteed a share in the next world. The Ben Ish Chai (Rabbi Yosef Chayim of Baghdad, 1833-1909), in his work Od Yosef Chai (Parashat Vayakhel, Halacha 4), adds that for this reason we recite at the conclusion of Ashrei the verse, "Va'anachnu Nevarech Ka Mei'ata Ve'ad Olam" ("And we shall bless God from now and forever" – Tehillim 115:18). Since we make a point of reciting Ashrei three times daily, we are confident that we will be privileged to praise the Almighty "from now and forever" – both in this world and the next.
It must be emphasized that whenever one recites Ashrei, he must concentrate with particular intensity while reciting the verse "Potei'ach Et Yadecha…"
If a Minyan has yet to arrive, may the Chazan begin reciting Ashrei, and then continue with Kaddish and the Amida when the tenth man arrives?
The Ben Ish Chai (ibid. Halacha 4) rules that the Chazan should not begin the recitation of Ashrei before a Minyan has arrived. Since the Kaddish is recited as a conclusion to Ashrei, a Minyan should be present for Ashrei just as a Minyan is required for Kaddish itself.
Later (Halacha 8), the Ben Ish Chai records the testimony of Rabbi Chayim Vital (Israel, 1542-1620), in his work Sha'ar Ha'kavanot, that the Arizal (Rabbi Yitzchak Luria, Israel, 1534-1572) would make a point of donating three coins to charity during Minha, just as he would during Shacharit. During Shacharit, the Arizal would donate the coins while reciting the words "Ve'Ata Moshel Ba'kol" in the paragraph of "Va'yevarech David." In Minha, Rabbi Chayim Vital recounted, the Arizal would give charity while reciting the phrase "U'masbi'a Le'chol Chai Ratzon" during Ashrei.
Summary: Ashrei is recited before the Amida at Minha, and, as with every recitation of Ashrei, one must ensure to concentrate on the meaning of the words, particularly when reciting the verse "Potei'ach Et Yadecha…" The Chazan should wait until a Minyan has arrived in the synagogue before beginning Ashrei at Minha. It is proper to donate three coins to charity during Minha while reciting in Ashrei the phrase "U'masbi'a Le'chol Chai Ratzon."