If you want to use your own basket for this (although you'll still need to get someone to sit underneath it with you), the Romantic Picnic Basket can be purchased for 10 Love Tokens from any holiday vendor. Buttermilk Delights can be found within the Box of Chocolates buyable for another 10 Love Tokens.
If you don't want to spend the Tokens, just sit down next to anyone who's dropped a Romantic Picnic in Dalaran, right-click the picnic basket, and then eat your Buttermilk Delight. If you do have your own Picnic Basket, drop it anywhere in Dalaran, and odds are good that someone will happen along to join you over the course of the holiday. Failing that, asking a nearby player usually works, although Dalaran's not quite as full these days. I'd advise doing this in the early portion of the holiday as a result, as the city will likely go back to being a ghost town as players finish off achievements.
My Love is Like a Red, Red Rose
Robert Burns is probably rolling over in his grave at the standard English spelling. For this, you'll need to nab a Bouquet of Red Roses or Bouquet of Ebon Roses drop, both of which will appear off a few specific 5-man bosses. Last year, you could get roses off:
Nation of Adoration (Alliance) or Nation of Adoration (Horde)
In each major city, Kwee Q. Peddlefeet will offer you a daily quest to bring a Lovely Charm Bracelet to the city's corresponding faction leader (e.g., Varian Wrynn in Stormwind, Garrosh in Orgrimmar, etc.). The quests aren't mutually exclusive -- you can bring a Bracelet to Magni Bronzebeard and then head for Kalimdor to give one to Tyrande all in the same day -- so the only limiting factor is how many Lovely Charms you've got on you. You'll have to farm 40 to make the necessary Bracelets.
The Rocket's Pink Glare
Love Rockets are purchased for five Love Tokens in packs of five. Once you've got 10, this achievement couldn't be simpler; drag them to one of your hotkeys and spam it until you've got the achievement. You should be able to shoot 10 off within 20 seconds very easily.
Players have reported issues with lag affecting their ability to get this, so if you're playing with high latency, you may want to get a few extra rockets just in case, go to an uncrowded area, and/or try this during one of your server's slower periods.
Easy, easy, easy -- as soon as you get the item you need. The Silver Shafted Arrow is buyable in packs of five for five Love Tokens (so 10 Tokens total). As soon as you've got them, shoot any player in sight who doesn't already have a noncombat pet out. Once you've got 10, you're all set.
The achievement doesn't work on players who already have a pet out because the Arrow gives the targeted player a temporary noncombat pet. Because you can only have one out at a time, the Arrow won't work on any player who already has one, so be careful if you're trying to shoot anyone in a huge pack where it's difficult to tell this.
All of the candies needed for this can be found in the Box of Chocolates you can buy for 10 Love Tokens. Stuff yourself with all four (you can combine the Buttermilk Delight pig-out with Lonely?, above) and you're golden.
Not required for the meta
There are some achievements related to the Love Is In the Air holiday that you can do just for fun and aren't required for the Love Fool title.
Lovely Luck is on Your Side
The Lovely Black Dress is indirectly buyable for 20 Love Tokens. What you actually do is buy the Lovely Dress Box, then right-click to open it. Please note that, even though the dress can be traded between characters, you will only get an achievement from looting it from the BoP Box that you'll obviously have to buy yourself.
Once upon a time, you needed to get very, very lucky with a Truesilver Shafted Arrow, which was a 1% drop from a Gift/Pledge from a city NPC or guard. Thankfully, these days they're buyable for 40 Love Tokens.
Working on achievements? The Overachiever is here to help! Count on us for advice on Azeroth's holidays and special events, including new achievements, how to get 310% flight speed with achievement mounts, and Cataclysm reputation factions and achievements.