So, aside from doing that /\/\/\/\
Think about why the intro is as far as you get?
Is it a case of
- fear of failure?
- fear of success? (opposite side of the same coin)
- mental blank?
- mental block?
- something else?
Most times you just need to bite the bullet and continue.
If you have an intro, then reuse it without the melodic material as the backing for the verse. Look into some ideas for switching it up for the chorus or the bridge (search on fp for many good tips already offered in that direction)
If you have many songs that are just intros, do what the Beatles did, take different tunes and combine them to make a bigger complete song.
Basically, you have to adopt an attitude that addresses your problem from a craft perspective rather than
an inspiration perspective; Thomas A Edison (the inventor) said that inventing is 1% inspiration and 99% perspiration: 1% spark and 99% effort moulding that spark into something worth selling.
The same is true of any creative activity: you need to realise that it is more about craft than it is about art - learn the tricks of how to manipulate your ideas into larger arcs of creativity, by learning the craft of arranging and orchestration, melodic development and harmony: these together give you a set of tools to apply to all of your creative endeavours, making you a better artist and a better craftsman.......