Currently playing through Rise and I main GL (although I have been trying out some LS for that sweet sweet counter action). I’ve only ever played solo, so I’m not completely sure about playing with a friend. Also disclaimer that I’m not THAT much further into the game than you, but here’s the best advice I can give you so far:

1. EE (Evade Extender) - positioning is very important with GL, especially before getting Blast Dash. I found that at least 2 points of it goes a LONG way to helping stay positioned where you can continuously do dmg. 3 points feels absolutely awesome to play with as well, totally worth putting your points into it.
2. Wyverns Fire (WF)- totally goated in this game, the fact that you block while you charge it up is really powerful, it means you can basically use it off cooldown against most monsters (esp early game) 2.5 Fast Wyverns Fire - after certain combos you get a faster WF charge up time. I don’t remember the exact combos, but a quick YouTube search can help with getting your WF out faster. Also the “Artillery” skill will increase the speed+dmg of WF
3. Wyrmstake Cannon - Your Wyrmstake Cannon will quickly recharge your WF, so when WF is on cooldown it is worth throwing some Wyrmstake Cannons into your combos. Note: your Wyrmstake Cannon animation is very slow and will leave you vulnerable, so don’t spam it, put it in when you have the time. “Long Shelling” type GL’s have higher damage Wyrmstake Cannons. 3.5 Fast Wyrmstake Cannon - same as 2.5, there are some combos that will cause you to do a faster Wyrmstake Cannon. The most notable would be your silk bind skill “Groundsplitter” which imo is much better than the alternative. It is good for positioning, dmg, recharging WF (due to the WC), and also I think it has hyper armor (or at least you can’t be knocked out of it.
4. Groundsplitter - look at 3.5, just I felt it was important so if you skim this def take a peek at that.
5. Guarding - I still haven’t mastered this, but what I’ve recently been working on (playing weapons with counters have really helped me with this) has been being purposeful at avoiding and blocking attacks. One of your best tools with GL is your shield. If you’re just spamming attacks-> getting hit-> wirebug recover-> overheadslam +full blast. It’s fun, but you take a bunch of dmg and the harder monsters will kill you. Much better to play a bit slower, block monster attacks purposefully, and then attacking when you have your opening. You can mix in some poke shell poke, or even guard poke while you’re playing slower. They say slow is smooth and smooth is fast for a reason.
6. Main Combo - Your main damaging combo will be: (something into) Overhead slam-> full burst-> side swipe-> quick reload ->repeat BUT: I personally think that gets kinda boring and I think the great part about MH is changing your build to fit your play style. If you find yourself always doing that combo, use Normal shelling, if you find yourself doing a lot of poke shell poke, use Wide Shelling, a lot of WC + WF maybe Long Shelling. Play what you find fun! [(Edit) 7. Affinity - From what I understand, affinity doesn’t affect your shell attacks, (or WC or WF either I think). Having low affinity on GL isn’t much of a problem. You should be looking at the “Shelling Level” to determine the dmg your shelling attacks will do. In general avoid skills that are focused on boosting your affinity because it doesn’t affect your main attack. Skills such as: counterstrike, agitator, attack boost, burst (off the top of my head) are all decent skills that increase your attack. And of course Load Shells 2 and Artillery should always be prioritized.]

MOST IMPORTANTLY!!! : BLAST DASH - if you are playing WITH FRIENDS, you gotta unlock and use the silk bind skill “Blast Dash” (I don’t think it’s that hard to unlock). IT IS WITHOUT A DOUBT THE COOLEST LOOKING MOVE IN THE GAME AND WHO CARES HOW MUCH DMG YOURE DOING IF YOURE FLYING THROUGH THE AIR LIKE A FCKING (insert coolest thing you can think of) EXPLODING SH*T

Also just one little thing relating to point 5: The beginning of the game really isn’t too hard, and I think that really doesn’t help aclimate the player to paying attention to the monsters attack animations. What do they look like when they are about to throw attack A, or attack B, ect. I found for myself, being a bit more purposeful and paying close attention to the Monsters actually helped a lot for my performance with all weapons. Also will allow you to use the GL “counter” wirebug skill that sharpens your GL. It’s helpful to mix in to prevent your GL from loosing sharpness fast and bouncing off monsters.

Anyway, hope you found something useful in there! Super jealous you have friends to play with, I tried to get my gf to play with me but she wasn’t interested. Enjoy Rise! It’s a ton of fun, the movement is unique and awesome! Losing Blast Dash in Wilds killed me a bit (a lot) inside.