After a while of measuring things you'll probably be able to eyeball a lot of portion sizes.
I actually never weighed anything (and I still don't) but I do occasionally measure. If I wanted to learn how much a portion size was, I googled it and looked at a picture. I knew I would get too obsessive with weighing.
When going to a restaurant, google the restaurant's nutritional information. They generally have to make it available, but if they don't you can find it on other websites. This is why I love having a smartphone—if you randomly go out somewhere you can still look up the info. I always add 100-200 calories to the count the restaurants show because they can be off by quite a bit.
If you're going to a Mom and Pop place, google a similar dish (or the components of the dish) to get a ballpark estimate.
The best thing though, when going out to eat? DON'T EAT THE ENTIRE DISH (unless it's from the low cal menu or something). You'll probably almost always be safe if you eat half or less of it. I know it can be hard when they bring you out a heaping plate of awesome food, but you don't need to eat it all.
One thing that worked for me when I started out was to ask the waiter/waitress for a takeout box as soon as I got my meal and immediately put half of it away before I started eating. It wasn't quite out of mind that way, but at least it is away and you can't pick at it. The bonus is that you get two or more meals out of a particular dish! Nice way to save money and time
Right now I don't need to do this any more and I haven't done it in a while. I find that I'm usually full after half a portion anyway and I don't feel the need to pick at it when it's sitting in front of me.
I don't necessarily agree with eating 5-6 meals a day; it really depends on your day and how you like to eat. DO drink plenty of water though; it can help fill you up and flushes out your body if you happen to eat too much salt in one day.
A lot of this is trial and error and finding what works for
you. Don't give up if you happen to go over your calorie count one day, just get right back on track immediately
Oh and relax

and have fun. One thing I loved about calorie counting is the freedom. I still went out to eat, I still could have everything I wanted...as long as I stayed in that calorie count!
Works for maintenance too, I'm pretty much doing the same thing just with a higher calorie count.