Make a simple sketch on a piece of paper how you want your piece of craft to turn out. (Especially the outline of your piece.) Glue it to your cardboard and cut the shape out (as seen in the bottom right of this picture.)

Next, gather 3 pieces of tissue paper. Have a palette, water colours and a few paintbrushes ready. Put pink and red colours into your palette and add more water, and use your paintbrush to spread the colour evenly on each tissue paper. If you are the impatient sort, you can just dip the tissue paper into the palette. Let the tissue dry, and you would get something like this.
NOTE: Of course if you have bold coloured tissue paper, you could skip this step entirely!

After all the tissue has dried, you can start to tear small coloured parts of the paper and roll them up into little balls (of doom). Separate them by colour so it's not too messy. Better to have more balls than not enough balls. Then you can start to glue these blobs to your cut-out! Be creative! Use different colour combinations and explore as well!

And, you are finally done! Yay!
NOTE: It can be quite tedious and messy from all the glue but it's definitely fun to do. Also you can find better use for this by attaching it inside cards and such? Have fun!