Here is C major scale representation from C to C (eight notes, 12 semitones):
It consists of 2 tetrachords 1_1_11:
If we divide every mode of the 8-note C major scale into 2 parts containing 4 notes each, how many groups do we have ? Only 4. Here they are:
1_1_11 or just 1-st
2_22_2 or 2-nd
33_3_3 or 3-rd
4_4_4_4 or 4-th
Each of this parts has perfect simple pattern and very easy to remember for a guitarist.
Here is how modes of C major scale are constructed:
1_1_11_1_1_11 or 11
2_22_2_2_22_2 or 22
33_3_3_33_3_3 or 33
4_4_4_41_1_11 or 41
1_1_11_2_22_2 or 12
From A (a minor scale):
2_22_2_33_3_3 or 23
33_3_34_4_4_4 or 34
I hope this will help you to memorize interval structure of all modes of any major scale very quickly so you can start practicing it.
Note the interval between groups where 4th group is present. It is a semitone, while it is a tone in other cases.