Never underestimate the need for accurate measurements in cooking. This can be especially true when baking. Liquid and dry ingredients are mostly measured by volume, although sometimes a recipe calls for measurement by weight.
Buying good measuring equipment for the kitchen is always a good investment. When baking pies, breads, or cakes, accuracy is very important if you want good results. Some measurement tests I've read have found vast differences in accuracy at times, so don't skimp.
Liquid Measuring Cup
Large cups are a lot more versatile than smaller ones. I like the two and four cup Pyrex models, but plastic will do. Some say that plastic is longer lasting and safer, but I've not found that to be true. I recently threw away some plastic ones I had when the bottoms cracked. Try and get one with both Standard (US) and Metric units.
Smaller measuring cups are fine for dry ingredients, and will work fine for smaller liquid measures. The base measure is the 8 ounce cup (250 ml). You'll want cups in 1, 1/2, 1/3, and 1/4 sizes at a minimum. I like metal ones, but plastic ones are okay, too. Measure all ingredients level with the top of the cup, or some other mark. Sliding the back of a table knife across the top is an old trick that can help remove the excess.
Teaspoons and tablespoon measurements should be done so the ingredients are level with the top of the spoon, just like the larger measuring cups. Metal or plastic sets are fine, but don't use the silverware you put on your table and eat with. It's just not accurate.
I actually don't have a set of these, but I'm beginning to wish I did. They can be useful for weighing meat portions, as well as fruits and vegetables when canning. Professional bakers use them because it takes into account the current moisture content in the flour, where measuring cups do not. I've been told that balance scales are the most accurate, but I'm not sure I believe it. The scales I used in college chemistry were digital and insanely accurate. In any case, when I eventually buy a scale, I think I'll go for a good digital one.