If your team doesn’t buy a courier and doesn’t ward, you’re probably gonna lose. Even if you aren’t a support but your team doesn’t buy a courier just suck it up and buy it yourself. Here is a little trick with the courier, you don’t need to go to the base yourself to spawn it. Just buy it while you are in the lane and right click on the courier and drop it from stash. Now anyone can just go to base and spawn it for you, and considering how your team was reluctant on buying one in the first place, its going to be very soon. Now for the wards, they last for a limited time so they constantly need to be replaced. You need to know what is going on in the river and the jungle because they are big blind spots. Without wards you are just asking to be ganked. To ward just buy them and place them on the giant eyes you see. A ward near Roshan is also essential mid game (or early game if they have an Ursa, as he can do a very early solo Roshan, with the right items).
And if you are laning against heroes who go invisible, buy sentry wards ASAP. Sentry wards can also “see” enemy observer wards which you can then swiftly remove, or just keep them there and fool the enemy into thinking you are stupid. If you lose a tower, place an observer ward where the tower fell just to know whats going on beyond your field of view. Also you should know that your field of view is reduced drastically at night time (except for a few nocturnal heroes). Lastly placing wards in the enemy jungle, will not allow the jungle creeps to spawn, hurting his early farm capability. I will go into detail about the best places to put sentry wards in the jungle in another guide.