Here is a breakdown on how to save everyone through the ending of Mass Effect 2 and get the No One Left Behind achievement or trophy. Apart from the ubiquitous revelation that you're walking into a suicide mission, there are no other spoilers here.

Most importantly:

• Loyalty: Get max loyalty with everyone to guarantee their survival. You'll be using a majority of your team in someway or another. It's imperative that you do this because normal/non-loyal team members are bad choices for any kind of mission (especially escort or your own team). Some people have reported success with non-loyal members on lower difficulties but it's very much a hit-and-miss kind of thing. Get your conversation hat on and get them loyal.
• Ship Upgrades: Get the following ship upgrades: Armor (Jacob), Shields (Tali) & Thanix Cannon (Garrus)
• Pick the right team: You have to choose the right people for every job. The selection is usually very limited and the following table can help you figure out who goes where.

The following factors also come into play:

• Weapon & Research Upgrades: Not a priority but it helps to research character specific upgrades like Jack's L5 Implants since it makes them more viable for their respective roles.
• Alignment: Your Paragon/Renegade alignment don't make a direct impact on who gets to live but they are essential in gaining your teammates' trust. Some dialogue options are only available at 75% or higher. If you lose the trust of a team member, you need 100% alignment to win them back.
• Specialists: Assign specialists for each job, hybrids don't cut it. The requirements for each sub-mission will be made fairly obvious to you by the game itself. Pay close attention to the dialogue options and choose carefully as to who does what. Refer to the following table if you need directions.
• Mission Dependencies: Often the success of one squad member will effect the life of another - all the sub-missions are connected somehow. Look at all your choices if you think a team member is dying in spite of being the right person for the job.

If you satisfy the above conditions, Shepard will survive. In addition, if you want everyone else in your team to make it through (for the achievement), these following approaches are known to work:

FAQs/More Strategies

• Dealing with non-loyal team members - Miranda/Jack situation - If Miranda or Jack (or any other character) are not loyal, they have a tendency to die during the final cutscene, even if you don't use them. Here is a possible solution that works on Normal difficulty - pick a weak final team and send a weak loyal character on escort. Recommended characters to take with you are: Tali, Samara, Thane, Kasumi, Miranda or Jack (who ever is loyal). Send someone like Mordin on escort as well. The aim is to leave behind a physically strong ground squad (characters like Garrus, Legion, Grunt, Zaeed). The reason is the game tallies up some kind of hidden score and your ground team's chances of survival increase if you leave behind more number of tough fighters. Just as an example, on my Insanity playthrough, I used Garrus+Grunt for the final battle and Mordin ended up dead. To fix this, I used Miranda+Grunt instead and everyone survived.
• Dealing with non-loyal team members (the lazy way) - You can always turn down the difficulty to Casual and not use the disloyal member at all.
• Random death of loyal team members - There are certain combinations where a loyal team member dies during the final cutscene for no apparent reason. I found that changing your final team can help solve this. Like the above case, a good general strategy would be to take a weaker team with you to the final battle; just make sure they are all loyal. For the rear guard, leave behind strong, combat focused characters that can hold their own in a firefight. Characters that work well for this are Grunt, Thane, Zaeed and Legion. Characters that have a tendency to die in this scenario are Mordin, Tali, Kasumi and Miranda.

• Trouble in vents ? - If your tech specialist is taking one in the head in spite of all the upgrades & max loyalty, try changing your 1st squad leader to Garrus/Miranda.
• Picking an escort - As long as the rest of the squads do their job perfectly, the escort choice is almost inconsequential. Just make sure he/she is loyal and they will all survive. It's a good place to send your wimpy characters to.
• Escort dying ? - In the odd case that the escort dies, try switching your 2nd (Fire) Squad Leader to a loyal Garrus or Miranda.

• Mordin - Quite a few people are having trouble with Mordin dying for no apparent reason, even with max loyalty and all. Try using him as an escort or even part of your final team to fix this problem.
• Saving the Normandy Crew (NPCs) - This depends entirely on how quickly you decide to use the Omega 4 relay. If you want to save everyone, use it as soon as it is available. The relay opens exactly one mission after the IFF and its recommended you use that time for Legion's loyalty mission. Any time wasted on side missions or other loyalty quests at this point will result in loss of lives. Your final team makeup will have no effect on who survives. The NPCs don't matter for the achievement.

Flow chart

The guys at Game Informer produced this flow chart back in June which presents the above information in a nifty format. You can view the hi-res version here (just hit the zoom in button at the center) or download it from the original GI article here.

If all else fails...

Turn down the difficulty setting from the Options > Gameplay menu. Team members with Normal loyalty have a higher chance of dying on the harder difficulty settings. If you just want the achievement or maybe want a perfect save game for ME3, just swallow your pride and turn it down to Casual. It might save everyone's hide.

Thanks to the GB community for all the feedback. If you finished the game, please do tell what worked (or DIDN'T work) for you and I'll add your strategy to the list.