Just do it.
It's a funny thing, even though we know something is good for us and even though we know we will feel better afterwards, the mind can still sometimes play games with us. Thoughts like "I don't have time to meditate"; "I'm too stressed to meditate"; and "I won't be any good at it" are all very common. Allow them to arise, see them clearly, smile at them for what they are -- just thoughts -- and then meditate anyway.