1) Book all accommodation weeks or even months before the walk as their are sections of the walk where accommodation is limited.
2) If you think your maximum walking distance per day is 12 miles, you will probably be able to do 16 miles, or pro rata, given that you have to walk those extra miles to reach your accommodation. You cannot stop on a desolate section of the walk and say "I cannot go any further".
3) Take plenty of water and drink before you get thirsty. If you are gasping for a drink you have left it too late.
4) Although our walk was principally to complete the Cleveland Way, if you wish to visit the various places of interest, then allow plenty of time for that.
5) We felt that walking 20 miles on our 4th day handicapped us on the remaining 4 days, a more equal daily walking distance would have been preferable but this is not always possible due to the location of accommodation.