The most under used item in every games (unless you have a really kind support or organize team) is ward. This item could make help you win games even if you are behind in kills and creep score. Especially when it come to late game where you might have lost vision from outer turrets, by putting ward at correct position you can ambush or caught enemy off guard when aiming for map objectives.
Most people will say that support need to buy wards for the whole team, while this idea is not 100% wrong at the same time it is not 100% correct as well. In my opinion, at early game every lane need to ward their own lane for their own safety from jungler gank that include ADC as well since sometimes support do not have enough gold to buy multiple wards. Once you reach late game ADC, AP Carry and Top laner usually do not have space for wards as they need to complete their fully build as soon as possible so in this case support need to pick the task to put ward for the team and jungler need to get ward as well if they have spare item space. Just remember support gain less gold through out the game and they will have less survivability as well on team fights, by picking up more wards they delay their timing to complete build.
Where to Wards?
Bottom Lane (Laning Phase)
Blue Side 1: if you only have 1 ward with you that will be the best place to put it as it will cover river(2), however it does not cover tri-brush(3) so be careful of gank from (3) if you push your lane to enemy tower. also this will give coverage of enemy support when they put ward. Do not worry to put ward in (1) if you are planning to put it on (2) and (3).
Blue Side 2: this will cover dragon area and if enemy jungler come from red side.
Blue Side 3: put ward in this place if you push your lane to enemy tower or you are being pushed into tower as mid champion like LeBlanc or Kassadin can dive under tower to kill you.
Blue Side 4 and 5: ward respectively if the enemy support is Blitzcrank or Leona to cover yourself from their skill shot and vice versa.
Red Side 1: same as blue side, however for red side it is enough to put on 1 since enemy jungler can only enter from river(5) and tri-bush(2).
Red Side 2: if the enemy jungler is Nocturne or Rammus, it is better to put ward in (2) as they can move/jump over ward coverage very quick and get to you. Also put ward on (5) to cover river side.
Red Side 3 and 4: same as blue side.
Red Side 5: mostly for dragon control, however put ward on tri-bush(2) as well.
Red Side 6: put ward here if you know enemy will tower dive you from behind.
Red Side 7: Only put ward here if you are being push to tower most of time.
Top Lane (Laning Phase)
Blue Side 1: most jungler will try to gank you once they clear their own jungle so they will come from tri-bush(1).
Blue Side 2: efficient way to cover yourself from gank as it cover river(4) and tri-bush(1).
Blue Side 3: put ward if you are being pushed to tower since sometimes they will let you push and have a jungler wait in the bush(3).
Blue Side 4: rarely I put ward in (4) on laning phase unless I know the enemy jungler will invade blue also put ward in tri-bush(1).
Blue Side 5 and 6: I won’t bother put ward in the side bush, unless I saw enemy jungler try to ninja his way to side bush.
Blue Side 7: put there if you are planning to invade red buff or you have destroy out turret.
Red Side 1: same as blue side (2).
Red Side 2: put ward if you are being pushed to tower or you are afraid being tower dive.
Red Side 3 and 4: same as blue side (5) and (6)
Red Side 6: I put (6) instead of (5) so ignore (5). Put ward in (6) if you are planning to invade blue buff.
Mid Lane (Laning Phase)
Both Side 1: put it there if you want to steal wraith camp and it also show enemy jungler movement.
Both Side 2: cover enemy jungler movement from bottom side. It will show their movement towards, (4),(5) and (7)
Both Side 3 and (4): if you can’t leave your lane to gank or steal neutral camp, put ward on both side to cover from gank or put 1 ward on 1 side and position yourself to farm near that ward.
Both Side (5): to cover your wraith camp from enemy jungler invade and cover your bottom lane from gank
Both Side (6) and (7): I rarely cover both side as it won’t give full coverage and early warning of enemy jungler movement, however put it there if you are going for dragon or baron as sometimes enemy hide in that bush.
Both Side A: put ward in these area if you have destroy outer turret and have advantage to caught enemy off guard and vice versa if you are in defensive position.
Both Side Red Buff and Blue Buff: put ward if you are planning to steal and kill jungler when they are doing their buff camp.
Both Side D: dragon coverage for team fight, if you get free dragon you don’t really need to ward every (D).
Both Side B: baron coverage, it is important to cover all area for team fight and avoid baron steal.