When dieting of course, you may need to take into account fat intake - fat contains a lot of calories. However I don't personally restrict the amount of fat I eat, and as a long term healthy eating plan I really wouldn't worry about fat from natural sources such as meat and dairy. Technically, the diet a creature exists on throughout its evolution should determine what is "good" and "bad" for it. Studies of bone from our predecessors showed that we mostly lived on meat, fruit and some vegetables, so it only makes sense that is a diet we should follow today.
Processed Food
You've probably heard everywhere to avoid too much processed food, and yes it does really make sense. Ridiculous amounts of random ingredients and additives, some potentially harmful, and less beneficial nutrients than fresh food. Processed food is definitely convenient, but not really the healthiest option. In fact I would expect that switching from a diet of mostly processed food to fresh, natural food would probably make you lose weight by itself. You've heard it a million times before, but fresh fruit and vegetables are essential for a healthy lifestyle. Frozen veg is fine, Although canned food and fruit is full of salt and/or sugar and is best avoided.
Portion Size
A bit of a no-brainer, but less food = more weight loss generally, although don't take it to extremes. The amount and frequency of my eating has decreased radically throughout the last 1 to 2 years. But instantly halving your food intake overnight could be difficult. I personally have gradually ate less and less over a long period, I still eat a reasonable amount but I only eat until I'm full, not just eating for the enjoyment of it. Don't worry if you find eating less difficult at first, just don't overdo it and your body will slowly adjust accordingly, and your appetite will drop just as mine has. I can't eat anywhere near the volume I used to be able to.
Stop looking at eating as an enjoyable activity. Don't eat for comfort. Food is a fuel. This is what I have started to realise throughout my period of dieting - food is necessary for our survival but gorging on it definitely isn't.
Plateaus
Argh, a dreaded word for dieters. A plateau is a term for when you stop losing weight for a period, and is the bane of losing weight. I have encountered many throughout my period of weight loss and my advice is to just stop worrying about it. Yes, you WILL start losing weight again, just give it time. What I've done sometimes is to actually eat slightly more than I was doing previously for a period, and then continue with the normal diet procedure, I think this temporary lapse in diet gives a kick up the backside to your metabolism and tells it to start working again.
Slip-ups
Yes, they're bound to happen. Giving into to your desire for some cake, or going out for a lavish dinner, or whatever it may be. If you have a bad day, or even week, don't worry about it. Let your diet lapse and perhaps put a pound or so back on? Well start again and you will probably find it comes off again easily, as your metabolism may have recovered a little from the harsh thrashing your diet may have given it. However, try and avoid too much yo-yoing; it's pretty harmful to your body and an excess of this could make it harder to lose weight in the future.
Exercise
Exercise has always been touted as necessary for effective weight loss. Well unless I'm an exception, no it really isn't. My level of exercise is actually embarrassingly low, I have never been to the gym, although I do walk a fair amount. And I have still successfully lost weight. BUT, exercise, as we all know, is necessary for long term health. That does not mean however that it has to be strenuous exercise, so don't think that - a lot of athletes die young so it can't be all it's cracked up to be. But regular gentle exercise has numerous benefits, and of course exercise during weight loss should speed up the process due to the expended calories, and increase your metabolism. Just make sure that the exercise doesn't make you so hungry you end up eating more, therefore completely wasting your time doing it in the first place.
Weighing Yourself
I weigh myself daily, but it's up to you if you would like to do it that often. It does however give an ongoing progress report, and is a useful tool. But there are some things to consider. Your weight will naturally fluctuate from day to day, so don't worry if you're a pound or so heavier than yesterday. I had a strange phenomenon myself - I would always weight a couple of pounds heavier on a Sunday - but be back to normal the next day. I never did work this one out. :) The amount you eat that day, and even the amount you drink can make your weight vary by as much as several pounds. Weigh yourself at the same time every day, either at night or perhaps better in the morning, wearing nothing, or at least only in underwear - even different clothes could affect your weight measurement.