Early in the game you usually want to be farming up your Seasoned Marksman for later in the game. Remember that this is for late game and your early game will NOT be good damage wise. If you're laning with someone, you will want to be healing them and poking people. Make sure to be aware of the map since you can help people out with your Sentinel.

If you're in a solo lane, just try and last hit and keep your lane close to your turrets but not too close where they use ammo. If you're pushed you will be overextended and you'll be risking being ganked. If you want to be pushed out make sure you use your Sentinel for vision if someone is missing. I prefer playing safer early since you don't have any escape and you'd be reliant on landing your Lunar Flare.

Arthas) If you're laning against Arthas, chances are you will be pushed up against your turret unless he's playing safe for a reason. If you want to engage on him, make sure to land your stun. If you do not land it, you will lose the fight. If that happens, just hit a Fountain and go back to farming safely. Make sure to dodge his snare and if you get hit by it before you stun, land stun and counter-engage. If he starts running I suggest leaving him especially if someone is missing since chances are he's baiting you to a fight you will not want to fight.

Falstad) When laning against Falstad, make sure to keep sidestepping to dodge his skill-shot. Remember that he has no way to regain his mana so if he's poking you a lot, watch his mana since you will be able to 1v1 him if he's out of mana.

Illidan) When you're laning against Illidan, you want to stay away from him and farm. Out of the three, he's the hardest to lane against. He will win most trades with Evasion. If you juke him to use it with a fake engage, then while it's on cool-down, you should be able to win a trade. Just remember to watch out since he has a lot of sustain with his abilities and auto attacks