You’ll see people doing various types of bridging exercises: sometimes with a ball between the knees and other times with an elastic band around the thighs. Depending on your needs, here is how you will choose the proper variation for yourself.
“I sit at a desk all day and have really tight hip flexors.” <- If this is you, grab a ball or fold up a pillow to wedge between your knees. Keep pressure on it – squeezing it – as you complete the bridge. This will force you to maximally open up through the front of your hips with each rep (improving your positioning when running).
“I have really weak hips and have difficulty standing on one leg.” <- If this is you, grab a looped band, slide it around your knees/thighs, and bridge up while keeping tension on the loop. This will help facilitate the continued activity of those supportive muscles needed for single-leg balance (or control during footfall when landing).
“I am both of those examples.” <- Then it looks like you have double-bridge-duty this weekend!