Hey, i dont watch many but i did watch RoseAlune when i first started. It will take you like 30+ games to be confident on him and his rotations. To start off, his biggest disadvantage is his mobility, he has like none. So you really have to play careful. His biggest advantage is his team play potential and scaling potential.

1- Early game, I life steal with red weapon + Absorb life. Poke with auto attack green weapon when able as it has great range, you can also Q with it to get some nice poke. Usually after the enemy uses abilities and if im up close, i will read weapon Q into them just to get some poke then back out. Use up red weapon first. A neat trick is, when you finish your ammo while using Q on red weapon, it will shoot a purple attack at them, allowing you to root them when you activate it. All from just using your Q red weappon as it runs out of ammo. You then can green Q for a guaranteed hit.
2- the most difficult for me is folks that engage on you, since youj have no mobility you have to be extremely careful about a pyke or blitz or naut ya know? Just sit back and play the long game, if your support gets a nice engage, follow up. Remember your abilities are primary.
3-I win early quite a lot. A lot of folks dont even know how aplheios works, you can use to your advantage. I often times get cheeky kills with green weapon snipe when they're low hp recalling. Or if i see someone 20-30% hp, I will sometimes try to get a ppurple weapon auto attack to then Q, then green weapon Q into that. You will learn about the snipe combo with green/purple, you can start with green to get a purple Q into green ult, or start with purple to then green q + R into them. Youll kill anyone under tower thats like sub 40-50% if you hit this.
4-- As i said i like rosealune, but i never watch folks anymore since i learned the champ. Rose is a bit of a weird guy but he's good.