Use a pink variation of rhubarb for a pretty coloured jam. You can, of course, use green rhubarb, but it will affect the final colour of the jam, turning it more into a greeny-brown colour instead.
Ensure you use a jam sugar when making this, rather than just a normal sugar. Jam sugar contains added pectin, which aids in its setting once cooked and is essential in one such as rhubarb, as there is less natural pectin in rhubarb itself.
Stir the jam often to prevent it from sticking to the bottom of the pan and burning. Always use a spatula or non-metal spoon with a longer handle and be careful of splattering jam as you stir.
I use a potato masher to mash up any larger pieces of rhubarb once it has cooked down and softened a little as I prefer my rhubarb jam more smooth than chunky.
Always sterilise your jam jars to help prevent the growth of bacteria. You can either sterilise in a hot oven for 20 minutes or pop the jar and lid into boiling water for 15 minutes before adding the jam.