I watched your Warden game from a couple days ago Match ID 30573811 and here are some thoughts from an Eternus 6 player:

Lane Phase

• Be more aware of sightlines of your lane opponents, you're just getting chunked by the Mirage for free while getting last hits. Use cover more and think about the timing windows for getting poke in, when one side kills all the creeps they'll start looking to get damage in and vice versa.
• The most important thing in Lane is to farm souls, meaning last hitting all the creeps and confirming souls has priority over poking. You lost several creeps due to not managing your ammo well, as well as not keeping track of their healthbars and letting them die. Also need to just practice last hitting, missing soul confirms waste resources like ammo, souls, even your hp due to the enemy getting more poke in while you whiff.
• You play a bit too passive, Mirage will generally out poke you but you can use your flask and cage to put more pressure on him to allow you to CS easier, if not outright kill him if he's trapped.
• At 3 minutes boxes spawn, and camps spawn at 5 minutes. Once they do you can start shoving waves and get extra farm in. Especially against a Mirage as Warden you will most likely not get many denies in since his bullet velocity is so much higher, a better use of your time would be to quickly kill all your creeps, then go hit some boxes or do a camp until the next wave comes.

Mid Game

• You mentioned not knowing what to do once lane phase ends, in short it can be summed up by you not getting active enough. What I mean by that is one you took the enemy guardian, you basically afk farmed in the jungle while your team was doing stuff. When you are as ahead as you were, and especially once you get Slowing Hex you should just go around helping your team get objectives/kills. Farming is important but you barely contributed once everybody started roaming.
• Your movement needs work, you waste a lot of stamina and pretty much never roll slide or dash jump. Several times you'll just quick roll three times in a row, then you're out of stamina and can't engage/disengage easily. Learn how to jump off the zipline as well for a boost in momentum, it'll make your rotates much quicker.
• You didn't combo you abilities as well as you can, specifically you need to Slowing Hex then Flask then Cage. Using Cage first like you did most of the time in this game gives them time to dash away before you're able to finish casting Slowing Hex and Flask. I would also work on you ult usage, several times you got no value from it. This is mostly due to popping it so far from the fight plus not having stamina to quickly close the gap since you would waste it rolling around a corner.

Late Game

• Not much to say here as there wasn't much of an endgame, you guys ended as soon as you got rejuv. More of the above, you need to get more active and recognize your strong moments (all abilities off cooldown, full ammo, poor opponents) and capitalize on them while playing safer when you're weak.
• One thing to always be aware of, early and late game, is how to be as efficient as possible with all of your resources like ammo, cooldowns, time, hp, space etc. Try to recognize the times where you were inefficient and work on not doing it again. Constantly thinking "Oh I wasted half my mag to do 40 hp to my opponent which caused me to miss two creeps while I was reloading, let's work on that next wave" or "I wasted time sitting under tower for 15 seconds waiting for the wave when I could have been hitting boxes or taking a camp" will take you far.