Major flow of the game so far-
1. Attack on earth
2. Flee from there to Mars to get Liara. She has info. on a weapon which can defeat reapers. Alliance will start it's construction and name it 'Crucible'.
3. Go to Council to get Support
4. Rescue Turian Primarch from Turian Homeworld Palaven
5. Host a diplomatic war summit between Salarians (Dalatrass), Krogans (Wrex), Turians (Primarch Victus) and Humans (You).
6. Get the Immune Female Krogan from Salarian Homeworld and get Mordin to work on Genophage Cure.
7. Cure the Genophage on Tuchanka. (Kill a reaper by forcing it to clash with mother of all thresher maws.)
8. Stop the coup attempt at Citadel. (Killed Udina, who was a cereberus mole and was trying to kill the council)
9. Go to Quarian's help, their flotilla is stranded in their Home system while attempting to take back their Homeworld from geth.
10. Resolve the conflict (I brokered peace between them and got both side to be my allies.) Took a reaper hands-on on ground with me targeting him with a laser and fleets firing on it from orbit. Felt epic after finishing it.
11. Go to Asari Homeworld for a crucial piece of 'Crucible' called the catalyst (Currently playing..
)
Along the ride there are many more priority missions in Tuchanka and Rannoch. Finish them first before the main one. Also on citadel, listen to people, would get numerous quests to boost your EMS (Effective Military Strength), mine is already full. But still it says chances to success in final battle are even.
Old acquaintances just keep going down, so far lost-
1. Mordin Solus (Inevitable perhaps) Sacrificed while curing Krogan Genophage
2. Thane Krios (Also inevitable) Sacrificed himself to save the salarian councilor.
3. Legion (Inevitable) Sacrificed himself to give all geth individuality.
Although saved Samara, she was killing herself.
Also found Jack, Jacob, Zaeed, Kasumi and got them as allied forces.
Miranda's story is a bit complex i think, still going on.
Kaidan Alenko (or Ashley for others) is a spectre and squad mate.
Got the Prothean General from 'From Ashes' DLC, he offers quite a prospective.
James Vega is good, but didn't like his personality.