One of the hardest parts for me about losing weight is eating out. My standard mindset seems to be that every time I eat out I can make it a "cheat" meal and treat myself to whatever I want. Don't get me wrong, I'm all about having a cheat day (only one per week!), and eating out is fine, but this is NOT a good mindset to be in when a dinner or lunch out pops up unexpectedly.
Even when I do try and make a healthy choice at a restaurant, I inevitably choose wrong - a salad that is a calorie bomb in disguise or grilled chicken that seems low cal, but is smothered in a calorie laden sauce. It's important to know exactly what you're getting when you order at a restaurant.
The trick for me is to always go in prepared. I usually have a go-to list of restaurants that I know what I can order there and how many calories it is. Panera, Subway, and Qdoba are some of my favorite go-to places. Thankfully, most restaurants have their nutrition information posted on their websites (except for the little mom-and-pop type local places), so it's easy to see exactly what you're ordering. Whenever I know in advance what restaurant I'll be eating at, I always take the time to look up their menu online. A lot of places have a low-calorie or healthy section of their menu that is worth taking a look at - Applebee's and Friday's for example both have "under 500 calories" options that are pretty tasty!
I usually try and go with the best low-calorie option that looks good. Occasionally, if I want to order something that's higher in calories, I'll make sure I don't eat as many calories for the rest of the day, or add a little to my workout to make up for it. And when I'm really wanting something that is pretty bad for me (i.e. a burger and fries or a big plate of pasta), I save it for my cheat meal (one per week!).
It's totally possible to eat out AND lose weight, it just takes a little research and a lot of self control.