I find it easier to always have the word above the code and to work down to encode and up to decode. Care must be taken to remember to reverse the direction of the rules, especially as the rules can be a mixture of - and +. This is why writing it down in the same format is important.
Ensure that when working out the rules you check each position - the rules can follow a sequence in the same way that VR Type questions do. Some examples of coding rules are:
Constant ... +1+1+1+1, +2+2+2+2, +3+3+3+3 etc
Increasing or decreasing ... +1+2+3+4+5, -5-4-3-2-1
Changing sign ... +1-1+1-1, +3-3+3-3 etc
Mixture of increasing/decreasing and changing sign ... +1-2+3-4
Another form of VR Type C is the Mirror Image.
In these questions, the alphabet is mirrored.
Any letter is encoded (or decoded) into its corresponding mirror letter.
A becomes Z,
B becomes Y, G becomes T and so on.
Another way to look at this is to divide the alphabet in two, between M and N and to count the same distance from the middle or ends.
A B C D E F G H I J K L M | N O P Q R S T U V W X Y Z
L is -2 from the centre so it will code into O (+2 from the centre). D is 4 in from the left so it will code into W (4 in from the right)
It doesn't matter which method you use - I find the 1st method much quicker (you simply write the alphabet backwards underneath the normal alphabet)
This form of Type C can be hard to identify. If you are struggling to find a code using the normal method it is probably because it is a mirror image type! I get my students to remember the first 3 or 4 letter combinations, A-Z, B-Y, C-X and D-W and look for these combinations.