How to make 1x buffer from 20x

As explained before here it is very simple and you need to understand the concept.
or you can use the formula M1V1=M2V2

Example

You have 20x Orange Juice and you wanna make 10 ml of 1x.

Simple use M1V1=M2V2

M1= Original Concentration [which is 20x]
V1= required volume to make 1x

M2= Desired Concentration [which is 1x]
V2= Desired volume which is 10 ml

20x * V1 = 1x * 10ml

V1= 0.5 ml of 20x concentrated juice is needed to add in 9.5 ml of water [10-0.5=9.5 ml]

IMPORTANT 

Don't add 0.5 ml in 10 ml. This will make final volume 10.5 ml and your concentration will be wrong.