[KarenO]

grass clippings make good compost when they break down but fresh green clippings do tend to form thick slimy smelly mats in between layers in a compost pile. What will help is if you allow even some of your clippings to dry into "hay" before adding them. now they are "browns" instead of "greens" use a long rake handle or pole to poke down through the layers from the top right through to the bottom to let some air in and water your pile if it's dry. should always be moist, not wet. A good sprinkle of high nitrogen granular fertilizer watered in will help your pile to heat and adding a little soil between layers as Redbaron suggests adds microbes which will speed up the composting process.
your compost will be like black gold for your tomatoes
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KarenO