We eat dinner together at the table Mon through Thursday (% of the time), and eat pizza and watch a movie or play a board game together on Fridays. Weekends are free for alls, at least where dinner is concerned. We currently have a 17 year old and a 13 year old. We have done this since we moved into our current home in 2009 (previous homes had no dining area). My kids are approaching adulthood and they are genuinely delightful to be around -- they are people I enjoy just hanging out with. I honestly believe our dinner habits combined with our parenting style is the reason they have avoided much of the teen drama.
It's habit, the kids don't even complain about it. We serve meals family style, so with two teen boys being at the table is the only way to ensure "dibs" on a favorite food item.
We adjust dinner times. When the kids were young and had evening things (scouts, club meetings, whatever), we adjusted dinner time for either before or after, with a snack to tide them over. Now, we tend to eat around 6 pm, which gives teens plenty of time to eat before heading out to hang with friends, study, and do teen things.
Dinner together doesn't work for over-scheduled families. If you have to be three different places every night, it fails. For us, we allowed kids two activities at a time, and one had to be low stress (an art club for one and an astronomy for the other -- both with infrequent week night requirements as events tended to be on Saturday's). DW and I are also self employed, so we have the luxury of adjusting our schedule. I recognize this is a privilege not all families have.
Finally, For us at least, family dinners work because I want them to be low stress. We don't enforce putting things on plates one won't eat. If you don't like something, don't eat it. If a meal isn't appetizing, the kids are welcome to grab leftovers or a sandwich and join us back at the table. My mom forced me to eat green peppers as a kid (and she still tries to this day...), the only food I truly dislike, and the smell of them still makes me retch. I won't do that to my kids. They aren't that picky, so it's not a huge issue, anyway.
We also don't enforce how long one sits at the table. You simply stay until you are done eating or ready to leave. Some days we sit at the table for an hour talking, some days one (or all) of us wolf our food down in 10 minutes then go off to do our own things. The important thing, to me, is that we made it a priority to take part in a basic human ritual that day, no matter how short. For us, this is dinner. For another family, it could be a family bedtime ritual, coffee and cocoa together in the morning, a daily "meeting" to discuss plans. I think the only important thing is that we carve out time, any time, to touch base all at once as a united family unit at least once daily (most days). It is what keeps us connected. It also shows our kids that they are important and that our time together as a family is a priority.