I think the short answer, in my case, would be: I don't.
I assume that the body changes over time. Even when my weight doesn't change, I find my shape can and thus the fit of garments is affected. Maybe I'm just an oddity?
Otherwise, I have many of the same strategies already mentioned, though I will say I'm actually not very good with 'good habits' alone --- I need it to be immediately rewarding in some way too.
For example, though overall I eat most like Denise (throw in a side of IK's processed carb avoidance), I find I am best off routinizing breakfast to 2-3 healthy choices each season. BUT, and this is crucial, I have to enjoy those 2-3 choices a lot, or I start craving a change. So I make my own muesli or granola tailored to my tastebuds, rely on eggs for a hot breakfast because I love them, and smoothies for summer. This is apparently my best bet for avoiding the lure of pancakes and traditional fried breads and things on a regular basis (I reserve those for travel and other times of day when I'm less vulnerable to 'lazy choices').
With exercise too, it has to be enjoyable even if it is a habit --- especially for a habit, or I won't stick with it. So a daily walk or swim is a habit, but I don't enjoy walking in wet weather or when it is excruciatingly hot and humid. For those days, there's music to motivate me, and maybe resorting to the treadmill in the gym to keep dry (and again, plug in the music). Finding a pleasant park to walk in goes a long way when I'm not in scenic surroundings.
And yes, I'm with Team 'Weigh Every Day'. I don't panic over the measurement, since I know what I ate, when I ate, the time of month all factor in. But it is motivation for declining the extra ice cream and choosing an espresso over a whipped-cream-topped confection.
Also, when I'm happy with my weight and shape, I reward myself --- not necessarily with food, but sometimes, yes, that too.
I also find avoiding boredom is a big one for me. Like Rachy's trigger is sitting down, I need to make sure I'm not bored --- especially not with food, or I'll try to eat more of it! So I make sure my meals are delicious. If I ate an unsatisfying meal, my chances of reaching for a treat to soothe the disappointment are a whole lot higher. Also, I NEVER tell myself I 'can't eat' X, Y or Z. Instead, I tell myself I do eat/love fresh fruit, salad, oatmeal with cinnamon on top, casseroles with half a dozen veggies, lentil soups...mmm! Focusing on the enjoyment of healthy food means I don't feel denied. Enjoying a pizza with friends means I don't stress about eating 'awful stuff' --- unless it tastes awful --- which in itself is a weight gain trigger.