Play it through a few times

Is it worth learning?
Do I like it?
Is the tune strong enough?

Assuming you have sensible answers to the questions

Transcribe the words longhand
Try to shortcut the writing stuff by using the Mudcat
(That failed last time and I had to transcribe and submit to the Mudcat)
Learn it one verse at a time
With luck the constant playing will have given you some of it
When you learn verse 2 put it with 1 and get a part song
and so on
Get half way then ignore the first section for a while and learn the last half (otherwise you practice the front end of songs far more than the back end)

Now what is it like
Can you sing it
If its not right can you make it right
If the answer to that is no then dump it you are never going to be comfortable with it.
Be honest with yourself

If its still good then practice till you really know it
You can start anywhere and still get to the end
There are no stops for thinking

You will not need a crib sheet for the words when you sing it
The words will come because its easier to get them right than wrong
Build up your courage and perform it.
Crib sheets are something between you and the audience so they may make you feel comfortable if it helps use them.

One thing not mentioned is there are times when your capacity to learn is at a maximum. For me thats the first few hours in the morning yours may be different.
Its worth finding out your best time it means you learn faster

Age has not proved a problem to learning or remembering but I do try to practice before I perform in public Insurance against stupidity

Fantum