When should you level it? I solo lanes 95% of the time cause I usually play 3v3, but should you put in 1-2 points at first or wait till your first 2 skills are maxed out?
it really depends... his wards are pretty great for pushing but his first two spells are great for killing... i would say it depends on who is laning with you and who you are up against and determine if you want to push or kill... if you are soloing i would get 1 level of it at level 4 to use as a sight ward in the woods around you... very useful for saving your ass
I only ever put a single point in it for a free 40 second ward. It's just not as useful as his other skills early game, when you should be ganking constantly, and later on the damage is pitiful compared to just autoattacking. If you wanted to push a tower early, you could put 4 points in it by level 7, but I wouldn't recommend it unless the other lanes are doing well and don't need you to help by ganking.
For slither, i usually dont get wards. However if their is a glacious on the team, i max it quick, just spam them and try and push the tower with the creeps.