I guess since Leon is going all out, I will throw down some real advice too.
Hotbar items - Figure out how to configure that. Items I usually have hotbar'd are Mega Potion, Dung Bomb, Antidote, Nulberry.
http://kiranico.com/en/mh4u Resource resource. You can look up items and it tells you where and how just about everything drops.
Athena's *** - I can't google a link for this while at work, but it is a nice little app where you can set skills you want, and it will show you different armor combos that get you there. You can save in your Talismans as well and it will be able to account for those which is nice.
Check out some weapon guides. Youtubers who I enjoy watching are Arekkz and GaijinHunter. Each of them has tutorials for every weapon type in MH4U.
At least get 1 armor set skill before you try playing online. Attack Up, Expert, even Defense Up or Health Up. Just something that shows other people you know at least somewhat how the game works. I seriously walk on matches if I show up and all 3 people have no armor skills.
Demon Drug and Armorskin - These are pretty easy to make early on. Always take at least 1 of each with you. This allows you to eat food in town with elemental resists and still get Atk/Def buffs. They last until you die or finish the quest so they are very much worth it!
Item sets and gear sets! I played like 40 hours before I realized you can make a ton of different item loadouts. This means you don't have to lug all your capture items with you when you plan to kill a monster or go on a gather quest. Gear sets are great because you might want to swap weapontypes based on your party makeup and it will save you a ton of time.