So I'm dipping my toe back into ME2 before playing ME3. I stopped just after getting Jack, and don't want to continue until I know what to do to get the best ending. Do I just need to get their loyalty all the way up? Do I do that by talking to them at every chance? Will my assistant alert me when they want to discuss something or do I need to do the run around after each main quest?

you need all the loyalty missions completed. To trigger them, you will need to initiate conversation with everyone at least twice, (I can't prove it, but I suspect you need to exhaust a few dialogue options with each) but after that Chambers should inform you if there's a loyalty mission available.

The best ending is also a result of careful preparations (ship upgrades which you'll get as a result of asking your squad about potential improvements), and then after a certain point, very careful timing and a few critical choices.

This FAQ is what I used in order to get everyone out alive. http://www.gamefaqs.com/pc/944906-mass-effect-2/faqs/59012

Loyalty with everyone, research all upgrades (the ones you get from the party members) and choose the following people in the final mission

• Tali for the Vent (apparently Legion can do this too but I've never tried).
• Garrus to Lead the second Fire Team
• Samara to protect you from the swarms
• Jacob to escort the crew back to the Normandy

Ensure that everything is done before the Collectors come and take the crew, when they get taken go immediately to the rescue.

Make sure you get the following items:

• Brandy for Doctor Chakwas
• Couplings for the Engineering Team
• Spices for the Cook

And be nice to Kelly, shes a lovely lady.

@the_great_skenardo said:

you need all the loyalty missions completed. To trigger them, you will need to initiate conversation with everyone at least twice, (I can't prove it, but I suspect you need to exhaust a few dialogue options with each) but after that Chambers should inform you if there's a loyalty mission available.

The best ending is also a result of careful preparations (ship upgrades which you'll get as a result of asking your squad about potential improvements), and then after a certain point, very careful timing and a few critical choices.

This FAQ is what I used in order to get everyone out alive. http://www.gamefaqs.com/pc/944906-mass-effect-2/faqs/59012

Is there a point in the story where there's no going back? I'm afraid I'm going to run into a Fable III like situation where I reach the point of no return without realizing it.

And be nice to Kelly, shes a lovely lady.

It's also super, super important to have your persona exclusively Paragon or Renegade. There will come a point (or two?) when two of your crew members will get into an altercation, and if you don't have the Paragon or Renegade points enough to use a Paragon or Renegade persuasion (that is, the blue or red dialogue option), then you will lose their loyalty.  
 
There are ways around the loyalty issue for certain characters if you still want to maintain a perfect ending. But that would probably require a guide or a FAQ. I could just spill the beans, but I don't know if you've played the game before and I don't really want to spoil shit you might not have seen yet.  
 
As far as a "point of no return" event--there isn't any time until the beginning of the final mission where the game sucks you through to the end against your will. That doesn't mean you can just fuck around indefinitely, though. There is a specific point near the end of the game where your crew is in peril and you have enough time between their initial endangerment and the beginning of the final run to do one mission without consequence, and you'll likely want to use the time to complete Legion's loyalty mission. (Again, I'm trying to speak vaguely. If you've played the game, then you probably know what I'm talking about.) If you dawdle here, your crew will begin to die.  
 
OH. Don't forget to upgrade your ship. Talk to everyone important on the Normandy about "Upgrades" and be sure to mine enough materials to equip the Normandy with the proper gear. It's easy to let one of those upgrades slip through and then pay the price for it without realizing you might've needed it. 

You need all loyalty missions and for an even better ending

Spoiler!

Rescue the crew right after they are taken.

@Barrock: There totally and completely is a point where there's no turning back. You will generally want to try and exhaust your loyalty/ship upgrade options before undertaking any major main quest undertakings.

The specific instance:

http://img203.imageshack.us/img203/3025/suisidemissionfinal8.jpg

This should help you a lot. Like others have said, do EVERYTHING else before you get the Reaper IFF.