As far as I'm concerned, there are 15 minutes out of every day that are good for meditation, and they are located in a fluffy cloud closet only found in the south of France. Since that doesn't exist and I haven't pinpointed the 15 minutes, nevermind the fact that you really need more than 15 minutes to meditate, here's a list of problems and suggestions to keep in mind when deciding where and when to meditate.

• Comfort V. The Deep Sleep
  First and foremost, whoever told you to meditate in full lotus lied to you. They hate you and talk about you behind you back. I can't even achieve full lotus, let alone sit in it for a half hour while I think about something else. You need to be as comfortable as possible, for as long as possible. Maybe you really like sitting indian style, but will you be able to sit like that for a long period of time? You might want to meditate within your cirle, but do you have room for cushions or a comfy chair? Hard surfaces don't tend to be good on your butt and soft grass has all manner of creepy crawlies to distract you. Do you have proper support for head? Holding it up on your own can become a challenge.
  Logically, you might be thinking that your bed is the best place to meditate. After all, you spend anywhere from 5 to 12 hours a night there. Unfortunately, trying to meditate in bed is like trying to watch a movie in bed; unless you are absitively posolutely sure you're not at all tired, you'll probably fall asleep before Sandra Bullock ever meets the guy she'll later hook up with. Go ahead and try it though, I've tried it more times than I can count. Still hasn't worked.
  Personally, the best position I've found is on my sofa. I sit upright with my legs folded on the sofa but not crossed. I wear light pajama pants so I don't feel restricted and I let my arms hang naturally in my lap. By staying upright, I know I won't fall asleep.

• Your family and friends are evil
  You love them, but you keep them around because they keep you entertained and they don't always know when it's not the time to entertain. If your significant other is as work, s/he will cal you as soon as you get comfortable. The baby will wake up from its nap. The kids will come home early from grandma's. Your friend's flight will be delayed. At some point in time, your loved one will interrupt you just when you think you're really gonna make it; try to take it in stride.

• ...so are telemarketers
  Unplug the phone. Specifically, unplug every single phone in the house. You know you have at least seven. Hell, I even have one integrated into my sofa. I have to unplug my sofa. If it's important, they'll leave a message. Chances are, they're just trying to sell you a bible.

• ...and your pets
  I love my Pheobe. She is cute and sweet and soft as a pillow made of cat fur. She'd be a perfect familiar if her cuteness hadn't rendered her completely stupid. But when I want to meditate, she wants out...and in, and out, and in, ad infinitum. The other cats want to eat, fight, or sit on my head. My dogs want to play fetch. The bird wants to talk to the outside birds. They don't mean to distract you but they don't know the difference. Unfortunately, I've found that the only way to combat this is to limit your pet intake. If you already have a dog or cat, consider your spiritual habits before getting another. Instead of a bird, get a lizard. There are no quieter animals than lizards. If you have a fish tank with a pump, keep it in a room you won't want to meditate in.

• So how about late night?
  I'm a night owl. It's not unusual for me to be up past 3AM. At midnight, I'm wide awake and ready to go. But I can't meditate then.
  When I lived in the city, there was just enough traffic in the middle of the night that there was always a car driving by, but little enough that I noticed every single one. When I lived in a college dorm, doors slammed, weird techno music played, and people frequently had sex. At my rural home, the crickets chirp all night long. It could be relaxing, but it's coupled with bullfrogs and geese. It's like trying to meditate in the middle of a cocktail party. If possible, aim for either 5AM or 2PM. If you can get up that early and don't have a job...