Blonde and Bof have both given excellent advice on how to succeed on an Audax, be it your first or hundredth. Perhaps it's worth elaborating a little.
Enter in plenty of time so you get the route sheet sent to you. Go through it, following along on a decent scale map of the area (1:50000 OS) and work out your route. Road atlas scales are not perfect at this stage as they may not show some minor lanes much favoured by event organisers! You will also get some feel for the climbs and terrain.
Once you are sure you have the route sussed, you can transfer it to torn out pages from the atlas as a way of economically taking a map with you. This is not only for getting back on the route should you get lost, but also to find a station, or a short cut home should you need to bail out.
I have even carried a OS map of particularly complex areas, especially if they come during the night towards the end of a very long event where getting lost might prevent me getting in 'on time'. The old coal mining area in Derbyshire on the way back to Alfreton is one area I remember.
Then you need a way of having your route sheet visible at all times. 'In a pocket' is rarely successful unless you are in a very simple area with few roads or on home territory. Some people put them on the top of a handle bar bag and others have some sort of handle bar mounted board. I made my from a couple of 'Space Bars' and a bit (3 x 6 inches) of 'House for Sale' sign. It was also useful for mounting lights when tackling night events. After that make sure the sheet is water proof and you have a way (headtorch) to read it after dark, if necessary.
As has been mentioned, the route sheets do vary in quality. Very few these days are plain inaccurate, but some fail to give the distance between junctions. Your pre-ride work with the maps solves both these issues, as you can add supplementary notes on the sheet.
The best route cards give a running total of distance covered and a 'split distance' between points mentioned. This allows you to relax a bit as your speedo will give you plenty of warning of the 'next' junction. I remember one ride where the route sheet took you through a town with plenty of instructions to 'take second right then second left', etc, coming thich and fast at about 200 metre intervals. It them said 'take next minor road on left', failing to mention this was in a further 12 miles! PPPPPP.
Admittedly, audax rides are low key and do attract more than their share of 'mature riders' who perhaps are overly wistful about the 'good old days'. But they are a great challenge and a good way of getting out and seeing new areas.