For your first walk try not to be too ambitious, pick something that is not too long and does not present any difficulty with navigation.
Look for a route that can offer a mix of different scenery and terrain as well as other items of interest such as view points, and the chance to spot some wildlife
for example, as you need to make the walk interesting and enjoyable for those attending.
When choosing a starting point for your walk you need to make sure that there is space for parking several cars without causing problems for residents in the area and if you intend to start from a pub or other private car park make sure you obtain the permission of the owners in advance, wherever possible it is best to use public parking areas.
Try to avoid if possible walking along busy roads as this can be quite unpleasant , country lanes are fine but you would not for example find it pleasant walking alongside the A47.
You need to make sure that any paths you intend to use are designated public rights of way as the appearance of a path or track on the ground does not mean it is a right of way and the last thing you want is an angry landowner on your heels. It is always a good idea to check any routes obtained from a book or other source against the relevant Ordnance Survey map.