In League of Legends there are things that will get your team ahead, known as "Objectives". These can be as small as neutral minions and buffs, and lead up to kills, Dragons, Towers, Barons, Inhibitors, and finally, the Nexus. When looking at objectives to determine how important they are and what tier they should be placed on, one must also consider the risk levels involved against the rewards. Also to be considered is what objectives will allow you to complete other objectives, and how many people are needed for each objective.
Tier 1 is the Nexus. This is the most important objective, and is worth infinite amounts of the other objectives as this objective alone will cause your team to win the game.
Tier 2 is Inhibitors. Killing an inhibitor will keep a lane constantly pushed with super minions. An inhibitor will allow your team to take most-all of the other objectives freely for a set time. While pushing an inhibitor, you have the option to back off whenever you want. If played right, Inhibitors offer low risk at high reward.
Tier 3 is Baron. Baron gives gold, experience, and a buff, and Baron may give a team the short term boost necessary to ace the enemy team and win the game. However, once you have gotten Baron low it is very hard to back off as you have already committed to it. Baron will get your team low as well, and fighting Baron and the enemy team will almost certainly result in your team losing. Baron is also steal-able, and for all of these reasons I say that Baron offers VERY high risk at VERY high reward.
Tier 4 is Towers. Farming in a lane with all the towers up is much safer than farming in a lane where towers are down. Towers also keep minions from pushing, which will allow your team to group up for objectives while your minions push and give your team map awareness of that lane. Towers also give gold, and the earlier you can get the boost, the easier it will be to get more items and take other objectives. Towers are the safest objectives in the game, and warding can allow you to push down towers with minion waves with you fairly risk free.
Tier 5 is Dragon. Dragon may look more important than towers simply because it gives more gold, but Dragon is far inferior to a tower. Dragon is extremely risky, as there are no minions to tank it for you like there will be for a tower. Whoever is tanking it (especially early game) might get low, and if the enemy team has a ward they can fight you over it and your team will be at an automatic disadvantage because you already have a weak player. Getting dragons will give whoever is at the dragon an experience boost and gold, but committing too many players to dragon may end up costing your team a tower if you leave lanes empty. My summary? High-low risk depending on map control, medium reward.
Tier 6 is a kill. A kill is extremely situational: Was the kill on a player who had a killstreak? Was the kill on a carry, tank, or support? Did whoever you killed have an oracle? Did the player have buffs? At what stage of the game did this kill happen? All these need to be factored in when determining the importance of kills, as a single kill can lead to Dragons, Towers, Barons, and Inhibitors. But generally, a single kill is less important than the other objectives, but may open up the ability to do other objectives. Going for a kill can also be risky depending on how much map control you have, and there is low-very high risk with low-very high rewards involved. Depending on the stage of the game, kills will go up a few tiers because they will allow for higher Tiered objectives to be accomplished.
Tier 7 is buffs. Getting your own buffs will give gold, experience, and a buff that will help a player to win the lane or win a teamfight, which can be really important. Also, denying the enemy team from buffs not only gives your team extra buffs and gold, but denies the enemy team buffs and gold. Depending on map control, the risk levels can range from low-high with low reward.
Tier 8 is other neutral minions: mini-golems, wraiths, and wolves. They give gold and experience to your team while denying the enemy team gold and experience. Depending on what neutral minions you are going for, the risk levels can range from low-high with low reward.
made from The Rain Man from Solomid.net