Everyones mood board will look different. And not everyone includes a mood board into the MDP. If you a feeling stuck just google 'mood boards' for inspiration.
Mood boards could include:
a) A colour palette: Squares of coloured paper. Painters samples. Squares cut out from photographs in magazines. Fabric scraps/ribbons/buttons/lace if a fashion garment.
b) Images of existing designs: Source magazines or scan images from books or the internet and identify what aesthetic features you like. You can use close ups of one detail that appeal to you or an entire product.
c) Descriptive Words: Open up a word document and type some words which suggest the feel of your product. ie Lush, Sensual, Mechanical, Elegant, Playful. Set them in a fontface that matches.
d) Textures: Walk around your school/house/ streets and photograph textures that appeal to you. Cut out squares of the photos and paste onto the mood board.
Also, if appropriate include references to a time period/style you are seeking inspiration from. Think of your target market in terms of likes and dislikes, ie a formal dress would call for imagery of handheld mirrors, lipsticks and ritzy cars. Use imagery to identify your target market and the environment your design will exist in.
Source your mood board cut outs from home and lifestyles magazines, fashion magazines, (or any that tailor specifically to your product), brochures, fabric scraps, your personal photographic library and assorted coloured/patterned papers.