To help the theme program run smoothly I buy 4 x 6 inch (10 x 15cm) cards and cut them in half to make 2 x 3 inch (5 x 7.5cm) cards.  I punch a hole in one corner and thread the cards onto a 25mm ring; they fit comfortably in the palm of my hand with my finger through the ring so I won't drop them.  

I write one song per card, colour coding as follows:

• Blue - is a brief summary of what I will say.
• Black - is any aid I will hold or place on the felt board as I am talking.
• Green - is the activity that the children will be doing.
• Red - is the song words written out in full including song number and book that it is found in; this helps if you have a mental blank.

I number the cards so that if I accidently drop them and the ring comes undone it is easy to put them back in the correct order.
When we have nearly finished singing the song I then flip that card over and glance at the next card to remind me of what will come next.
The cards are small enough to fit in the palm of your hand so they are not intrusive to anyone else watching.
 
TIP: When I first started using cards I was placing two songs per card and not cutting them in half, but discovered that occasionally I would miss a song out.  Having only one song per card has resolved this problem.