Wait until tzais hakochavim before daavening Maariv of the 50th day of sefira. This will complete the count of 49 days — ‘t’meemos’. (MB1)
Most Torah learners are awake all night involved in Torah study. This is a tikkun and can grant a person a guarantee to live out the year with no harm. (MB1)
If you stay up all night, do not say Al Netillas Yodayim unless you go to the bathroom before Shacharis. Then say Al Netillas Yodayim and Asher Yotzar. (MB1)
The entire Hallel is recited. Akdamus is customarily recited just before the Cohen blesses on Krias Hatorah. (ShA1)
On Shavuos, the Asserres Hadibros are read with taam elyon which makes each dibbur one single possuk. When read during Parshas Yisro and Voeschanon, read them with taam tachtone. (BeH)
Tachanun and voluntary fasting is suspended from the beginning of Sivan until the 8th of Sivan which is after Issru Chag. (Rama3 — MB7)
There is a minhag to spread out grasses in shul and at home to remember the grass on Mt. Sinai. This can be done on Yom Tov itself because the grass is not muktza. (Rama3 — MB9)
Do not put trees into shuls and houses on Shavuos — it has become a goyishe minhag. (MB10)
Other minhagim are to eat milchigs on Shavuos and to eat honey and milk because the Torah is compared to both. One reason for eating milchigs is to force you to bring out another loaf to eat with flayshigs — this is zaycher for the Shtay Halechem. Be sure to change the tablecloth for flayshigs, and rinse and wipe out your mouth. (Rama3 — MB13,15,16,17)
Yizkor and Av Horachamim are said on the second day of Shavuos. (MB17)
