One drawback of going on a low-fat diet for some people is that it lowers HDL levels. If raising your HDL cholesterol is a primary concern, you should replace carbohydrates in your diet with fats, preferably mono- and polyunsaturated fats. But avoid trans fat, which can lower HDL levels. These steps can lower both total cholesterol and LDL and maintain HDL or boost it slightly, improving the ratio of total cholesterol to HDL.
You've probably heard that fried foods of all kinds, hydrogenated oils, and full-fat dairy products are cholesterol bombs that are best avoided (and not just by those watching their cholesterol levels). The American Heart Association recommends that everyone restrict these foods, as they contain trans and saturated fats, the "bad" kind that raises LDL cholesterol and leads to plaque buildup in the arteries.