My best trick is to do a really low cal breakfast (usually under 200 cal). I like doing either two scrambled eggs without bread (Sainsbury's Medium Woodland Eggs are about 77 cal each, bringing you to around 150 cal). So you could even add a slice of bread there and still be at 250.
Or the Quaker Porridge Sachets come to about 180 cal and are also very filling. (I've also worked out that 30g porridge is 1/3 of a cup, so I tend to just do that to save me money and dicking around with scales).
Cutting carbs is my second tip to save calories. Courgetti in place of pasta gives you most pasta meals for 300-500 calories. Spaghetti bolonaise, avocado pasta, leek & creme fraiche & bacon. And it's way healthier.
Or just focusing on the meat, and filling the rest of the plate with vegetables. Stuffed chicken breast, or roast chicken thigh with Mediterranean vegetables. Pork in a mushroom sauce. Steak, garlic carrots, leeks.
Fish cakes are quite calorie 'cheap'. And soup is an obvious one, and really easy for lunches.
Hope at least some of that might help. I snack on Light Babybels (50 cal), natural yogurt with homemade plum compote or tart spiced, stewed apple, fruit, little packets of roast chicken from the supermarket, Cadbury's Highlights Hot Chocolate (like 39 cal, I think), squares of dark chocolate, Propercorn Popcorn.
My walk into Uni takes me past a Hotel Chocolat who almost always have free samples out so I can sneak in and grab one chocolate which is usually about 50 cal. Politeness prevents me from eating more 
. One day they'll start recognising me and I'll have to give it up.