Four interesting halachot relevant to Ashkenazim this year, since the 33rd day of the Omer falls straight after Shabbat (and on Sunday)
1. The Rema rules that it is permitted to have a haircut on Friday (but not Thursday night) "lichvod Shabbat" (Orech Chaim 493:2)
2. Even though it is permitted to have a haircut before Shabbat, weddings (and presumably live music) are permitted only on the day of Lag BaOmer (i.e. Sunday) and not the night before (i.e. Sat. night) (Mishna Brura 493:10 in the name of Eliya Rabba)
3. The Rabbanut of Israel has ruled that all bonfires and celebrations should be pushed off to Sunday (instead of Saturday night) to minimize chilul Shabbat (this applies even in neighbourhoods where the majority of people keep Shabbat).
4. Laws of Nezikin/Damages still apply on (and before) Lag BaOmer. If you are unsure of how to tend a fire and are not prepared (or able) to watch it until it is completely extinguished, do not light a bonfire. Leaving it under the supervision of a child is negligent and one is liable for any damages caused (not to mention the potential risk of pikuach nefesh in such a situation). Similarly, wood taken/borrowed/stolen without permission is forbidden to be used. Learn Bava Kama before lighting any fires. If you see others acting in a way which is irresponsible and/or assur speak to them and explain the halachot. If they do not understand, call the fire brigade (or police). Last year seven people were injured on Lag BaOmer. Each of us has the responsibility to ensure that nobody is injured and no damage caused to property this year.