There are four levels you'll have to complete on 007 difficulty with all the optional objectives for this achievement. I'll just cover the optional ones in this guide.
* Recover the Interrogation Footage: Near the start of the level, you'll come to a security checkpoint room which has a switch you'll need to activate in order to release a barred security door to progress through the level. In this room, you'll get a call from MI6 noting that you need to get a copy of the interrogation footage to prove your innocence. To do so, find the reel to reel tape recorder in the room and use your phone to record the footage.
* Destroy the Servers: When passing through the level, you'll pass through a room with a bunch of server towers inside. Shoot all of them until they explode to complete this objective - you'll know you're done when "Objective Completed" pops up. (Note that a few of them are located in a locked room which you'll need to access by going through the vent shaft nearby on the same floor, located near a dead plant and some cardboard boxes. Also note that destroying these within 40 seconds will net you the "Secret Servers" Achievement - start with the servers in this room to make it easier.)
* Gather Russian Intelligence for MI6:
** Part 1: One floor above the server room is a locked office. Immediately next to it is an unlocked office - enter and look at the walls to find a vent shaft partially obscured by a cabinet. Go next to the cabinet to get a prompt to move it, then crawl through the vent shaft to enter the locked office. On the desk is a computer which has some intel.
** Part 2: After receiving the call from MI6 ("I'll get back to you!") you'll enter a giant room. Progress through the room, dealing with special forces soldiers rappelling through the windows, until you come to a bridge above you with a flight of stairs in front of you. Hug the left wall, and in an alcove next to a weapons crate is a microfiche machine. (For the younger folks out there, it looks like a computer with a tall, skinny screen.) Activate it to scroll through a few articles until one showing the climate change facility shows up - you can now photograph this for the second piece of intel.
** Part 3: After taking the elevator to the basement, you'll come to a two-story garage. On the second floor, there's a hologram of a tank. Activate the hologram, and some schematics will come up - you can now photograph the schematics for the final piece of intel.
Tank: Just complete this level on 007 difficulty, as there are no additional objectives.
Train: Just complete this level on 007 difficulty, as there are no additional objectives.
* Obtain Intel on Janus Technology
** Part 1: After coming out of the sewer, a car will drive over the grate and three men will enter a building. Use the nearby ladder to climb to the roof of this building, and smash the skylight to enter the locked room in the back corner. Find the crate marked "Drone Gun" and activate it to open it - you can now photograph the first piece of intel.
** Part 2: After locking down the staging area and getting the call from MI6 ("The girl is expendable.") a bunch of thugs will breach the room that you've locked down. Once you've dealt with them, go through the hall where they breached from and turn right to see a weapons cache behind a fence. Take a photo of this for the second piece of intel. (Note: It's a good idea to take a silenced Ivana located on your side of the fence to help with encrypted transmission objective.)
** Part 3: After getting the call from MI6 about detecting an encrypted transmission, you'll enter a warehouse with many guards. Take all the visible ones out silently from the balcony where you enter (to help with the other objective), then go down onto the main floor and look for an open crate with some VCR-like objects inside. Photograph this for the last bit of Intel.
* Record the Encrypted Transmission: This one is tricky. In the same warehouse where you got the final piece of intel, you'll need to take out all the guards silently except one. (If you're detected in the warehouse, the transmission will immediately end and this objective will be failed.) The one guard you need to leave standing is the one listening to the transmission, and he's located in the high part of the warehouse, standing still. Get close to him without being detected, and you can use your phone to record his conversation. Once you complete the objective, you can subdue him and finish the level.
Hope this helps!