Hilchos uminhagei Shavuos 5786 (For reference only) 

- This year we make an Eruv Tavshilin on erev Shavuos since the first day Yom Tov is Friday. there are those who make sure not to eat the seuda too late after plag.

 Zman ט' שעות is 4:32pm

In Eretz Yisroel this year some shuls will lein the entire parshas Naso by Mincha on shabbos 2nd Yom Tov for bnei chutz Laaretz.

- The shabbos candles should be prepared ahead of time on the first day or prior to YT.

- poskim discuss taking a warm shower on the first day Yom Tov lekavod Shabbos. Ask you LOR

- On Shavuos at night the minhag is to wait until it is night (Tzeis Hakochavim) to daven Maariv in order to have 49 complete days. Shulchan Aruch w/Mishnah Brurah 494:1. BMG davens at 72 most shuls daven earlier 50 0r 60  minutes after shkiah.

(some poskim say that women should wait until it is night to light candles and say Shehechiyanu on Shavuos night. Luach R' Yechiel Michel Tukatchinsky, Piskei Tshuvos 494:2)

There is a minhag (brought in The Zohar) to stay up the night of Shavuos and learn Torah. This is based on the Midrash which says that Klal Yisroel overslept the night before Matan Torah and Hashem had to awaken them to receive the Torah. Therefore we stay up all night to rectify their oversight. Shulchan Aruch with Mishnah Brurah 494:1

 The Ari'zal writes that one who does not sleep the night of Shavuos and toils in Torah is assured to live out the year and no harm will occur to him. Shulchan Aruch with Mishnah Brurah 494:1

There is a compilation of torah learning known as "Tikkun Lay'l Shavuos" which has The Zohar and the writings of The Ari'zal as its source, and many have the minhag to say/learn this on Shavuos night. Kaf Hachaim 106:7, Lev Dovid L'Hachidah.

 Generally women should not say the "Tikkun Lay'l Shavuos". However, some say that a woman who counted all the days of Sefiras Ha'omer may learn the portions of the Tikkun which are from Tanach. S'U Rav Poalim 1SY:9, Kaf Hachaim 106:8

 One who stayed awake all night of Shavuos should immediately, at Alos Hashachar wash one's hands for Netilas Yadayim without a beracha, and listen to Birchas Hatorah from someone who slept, before one continues to learn.

Shulchan Aruch 4:14, 47:12MB28

 Before Shachris one should use the restroom, wash his hands and then make the berachos of "al netilas yadayim" and "asher yotzar". Shulchan Aruch w/Mishnah Brurah 594:1

 One who stayed awake all night should not make a beracha on his tzitzis. Rather, he should make the beracha on his Tallis Gadol and have in mind to be yotze for his tzitzis with the same beracha. Shulchan Aruch w/Mishnah Brurah 494:1

 One who stayed awake all night should listen to the berachos of "Elokai Neshama" and "Hamaveir Shayna Mayeinoi" from someone who slept during the night.

Shulchan Aruch w/Mishnah Brurah 46:MB24

 One who goes to sleep after Alos Hashachar Shavuos morning (or on any day) does not say the beracha of Hamapil. Shulchan Aruch w/Mishnah Brurah 239:1MB8, Piskei Tshuvos 494:5

 There is a well known minhag to bring flowers into shul and one's home as a remembrance that on Shavuos we are judged on "Peiros Ha'ilon" - fruits. However, one should not cut off branches from fruit bearing trees for this purpose because of the Torah prohibition of "Bal Tashchis". (Shulchan Aruch w/Mishnah Brurah 494:3, Piskei Tshuvos 494:10)

 There is a (not so well known) minhag to bring good smelling grasses into shul to be passed around for people to make a beracha and smell the grass in remembrance of the Simcha of Mattan Torah where Har Sinai was surrounded by grass.

(Shulchan Aruch w/Mishnah Brurah 494:3)

 Many have the minhag to eat a milchige meal (and milk and honey) on Shavuos. Some eat milchig at night and fleishig at the day meal, while others eat milchig, bentch, and then wash again, and eat fleishig to be yotze Simchas Yom Tov with meat.

(Shulchan Aruch w/Mishnah Brurah 494:3)

 If one eats milchig but not "hard cheese" (which requires one to wait six hours before eating meat) one need not bentch and wash again before eating meat. However, one should wash his /her mouth well and the tablecloth should be changed. (Other poskim require one to bentch).

(Shulchan Aruch w/Mishnah Brurah 494:3, Piskei Tshuvos 494:12)

 -One should be careful not use leftover challah from a milchig meal at a fleishig meal. (This is applicable all year as well). Rather, one should use new challahs for each meal. This also fulfills the minhag of remembrance of the Shtei Halachem (Two Loaves) brought on Shavuos in the Beis Hamikdash. (Shulchan Aruch w/Mishnah Brurah 494:3)

 We read Megillas Rus on Shavuos because it was written to document the yichus of Dovid Hamelech and (according to one opinion) Dovid Hamelech was born and niftar on Shavuos. (Shulchan Aruch w/Mishnah Brurah 490:9, see also Shaarei Tshuvah 494:3)