Fable II

Simply target (left trigger) and press Y to find out their perfect spot, perfect expression or perfect gift.
Then, get them to follow you there, when there, perform the perfect expression or give them their perfect gift if that didnt work.

All cred to Caltrop for this. Just wanted to get this on the tip page instead of the comments. A really easy way to get this is to use Alex from the Till death do us part quest. Just get her out to the clocktower in bowerstone and do a perfect bloodlust roar on her. Don't know why because its not her favourite expression but it does work. You can do this after you marry her aswell.

If anyone is still having trouble with this, here is a specific person to get it easily with.

Go to Fairfax Gardens. Make sure Brightwood Tower is a registered location on your map.

Find a plump, purple dress wearing woman known as "Sabine The Aristocrat".

Her location should be Brightwood tower and she likes two expressions:

1) Seduce
2) Heroic Pose

Get her to follow you. Fast travel to brightwood tower. Go up halfway through the tower (you may hear her say she likes the location). Do Seduce. Then do and extend till green Heroic Pose.

Bingo. achievement unlocked.

Just make sure she does not have a heart above her when you first find her.

The guides already posted are great but I would like to explain the process in more detail because I'm being requested to help with this one a lot in my Fable II sessions.

The short version:
You must take a person to his or her favorite place or region and use that person's favorite expression that is extendable. The person must not be in love with you (they must not have a red heart above them) but they must like you enough to follow you. It helps if you walk to the place instead of fast-traveling.

The long version:
Highlight a person using LT and then press Y. It will show his or her name, personality, likes, and dislikes. Not all of a person favorites are listed, especially when it comes to expressions. The important thing is to find someone with a favorite place or region that you know how to get to.

Use a quick rude (or failed) expression or two if the person is already in love. Be careful though, someone who is raunchy, randy, unchaste, or aggression-loving may only love you more! Some examples of a few easy dates include Tom the Stall Vendor, Claire the Jeweller, Alice the Stall Vendor, Biff the Blacksmith, Sophie the Aristocrat (if you've beaten the game), Chumley the Aristocrat (if you've beaten the game), Becky the Gypsy, Chik the Gypsy, Tim the Gypsy, Durril the Stonecutter, Alan the Gypsy, Jack the Farmer, Rick the Stall Vendor, Isaiah the Farmer, Seth the Farmer, Becky the Barmaid, Angus the Farmer, and Kiernan the Barman. Just keep looking at each person until you find one with a place you know.

If a person has a favorite place but not expression, perform "good" expressions like whistle, heroic pose, dance, victory pump, etc. and you'll eventually find one that gives a gold heart. Just make sure the expression can be extended into out of red into green. If it is automatically a success such as thumbs up, it will not work for the achievement.

If it does not pop, make sure you are in the right place. If you are, try walking out of the place, and then back in. Your date will mention that they like the place or that they like it over there. Make sure that they are following you and not dismissed. Make sure you don't scare them such as spellcasting.

Tried for hours, the other solutions don't seem to work for a female player character. After several fails finding someone in Bowerstone, I popped over to Bloodstone Water Front. The town crier there liked the boat house (100 feet away) and heroic pose. Took him there, did the emote twice, finally popped.