Many rooms in Warframe are standardised. Capture, raid, deception, defense (mobile and normal varieties), reactor sabotage, rescue and assassination missions all have standard objective and extraction rooms, depending on the tileset (i.e. map). Storage Containers and lockers will be found in the same or similar locations as previous encounters with any particular map.
Environmental Hazards (Fire and Ice)Sometimes the Lotus will say, "The cryogenics core on this ship has malfunctioned. Expect colder than normal temperatures." or, "This ship has taken some hits. Stay away from heat." This means there is either fire or ice on the level. Ice means your shields are halved. Fire means two things. Firstly, there will be fire patches on the ground. Stepping on them will cause you to take 50 damage every 3 or so seconds. Secondly, there will be Grineer Sawmen corpses lying throughout the mission. These can be looted using the action button (default X).
Enhancements are also very important items. Sadly, they are much harder to obtain. Orokin Catalysts can be applied to weapons (including sentinel weapons) and Orokin Reactors can be applied to warframes and sentinels. What both do is that they double the current mod capacity of the item it is applied to. They cannot be removed, but at least you do not need to worry about when to apply it. It will always double your mod cap. Forma, on the other hand, can only be applied to rank 30 items, and doing so resets the items rank back to 0. But it allows you to add or change a polarity slot of that item. Using a Forma on an item with Catalyst/Reactor will not remove it. Forma are also used in building rooms in your clan dojo. DO NOT waste your enchancements (unlike a friend of mine, who used catalyst on two of his starting items, skana and lato) as they are not easy to get.
Afuris, Akbolto, Dual Broncos and Twin Vipers. These 4 (or 8) weapons are different from the other dual weapons. While the other duals can be bought/crafted outright, these 4 need 2 of their single cousins, plus an Orokin Cell, to craft. To craft Twin Vipers, you first need to craft two single Vipers. The total cost of 115,000 credits is needed.And a single Bolto needs a Lato to build by the way.
Defense Missions (The Reward System)
Doing Defense Missions, also known as Endless Defense, is the best way of getting a large amount of mods, along with other good items. The rewards at the end of every fifth wave vary, so let me explain. Tier 1 def missions offer tier 1 rewards at wave 5 increasing by 1 tier every 5 waves. Tier 2 def missions start at T2 rewards on wave 5 increasing in the same way as T1. Tier 3 def missions offer only tier 3 rewards. Go to Endless Defense for a list of all defense missions and their respective tiers.
Alerts are a great way of acquiring certain weapon blueprints and Alternate Helmet blueprints. But if you have access to a cellphone, and the cellphone has access to the internet, do region chat a favour and follow @WarframeAlerts on Twitter. It will tell you what the ? reward is (if there is one). Then you won't have to ask. If you need an invite to that alert, then use recuiting chat.
Void Missions (Traps and Puzzles)
The Orokin Void is such a beautiful place. Too bad it's corrupted and filled with booby traps. Well there are tons of goodies to get (Primes), as well as a large paycheck for completing Void missions.
Affinity and Mastery Rank (Levels and Ranks)
Using a weapon. Correction. Killing things with a weapon, earns you affinity. Affinity levels up your equipment. Affinity Orbs also gives you affinity. Each time you level up a weapon, you get 100 points towards your mastery rank. Each time you level up a warframe, you get 200 points towards your mastery rank. Note there are some limitations. Firstly, Sentinels and their weapons do not earn you any mastery rank. Secondly, re-leveling equipment (selling, buying and re-leveling) doesn't grant any mastery rank. Thirdly, polarising equipment (Forma) and re-leveling it doesn't give any mastery rank.
Stalker (Why are the lights flickering? Who is this guy?)
Stalker is the Slenderman of Warframe. As the name implies, he stalks you. What the name does not imply, is that, upon arriving, he will bludgeon you to death. Stalker can only come after you if you have killed at least one boss, so, unless you only do the first 5 Mercury missions, he always has a chance of coming and brightening your day. However that chance is pretty low. But there is a way of increasing the chance of him popping in for tea and cake. You have to kill more bosses. As many as you can. When he comes, the lights will flicker and he will knock 3 times, each time saying some magic words. After knocking, he will appear in a cloud of black smoke and start running around killing everything. Should you not find him good company, you can tell him to shoo, by reducing his life to 10% or less (Melee attacks are not recommended, and he is immune to many abilities). Upon leaving, there is the tiniest of chances of him leaving behind one of three very special items, Dread, Despair and Hate. (Fluff Warning) You will also receive a Noddy Badge in Recognition of your Participation in the Event of the Twin Moons, Hosted by The Organisation of Bananas, who are dedicated to the Conservation of Llamas and Gravity.