Trim it, wash it and chop it into pieces. Here is my top tip for cooking Rhubarb, I do not add any water or 'Sugar' but I mix it with two or three good tablespoons of Golden Syrup. (If you are trying to cut down on sugar - no sugar fizzy lemonade or ginger beer is good.) I then put it in a medium oven for about twenty minutes. It still keeps its shape rather than stewing down to a puree.
For the crumble topping:
175g/6oz Flour
75g/3oz Butter or margarine75g/3oz Sugar
I rub the flour and fat together until it resembles breadcrumbs and then add the sugar. Place the crumble topping over the fruit and bake in a medium oven for a further twenty minutes, until golden brown. This crumble has been consumed with 'Toffee Ice-cream' or but my youngest stuck to his usual... 'Squirty Cream'.
When I was a child a comedy show used to be on tv on Sunday afternoons. It was called 'Rhubarb, Rhubarb'. The only words spoken for the whole show was 'Rhubarb'. I used to find it fascinating.