Sometimes you need to make a small digi item like a signature, blog header or FB cover photo and you can't start with the 12x12. You might just start with the size you need but now you have shrink all of your kit elements to fit on that small shape. There IS a better way! Start with the similar dimensions as big as you can and then create your image there, resizing the final product! Here's what I mean and I use math to figure it out every time!
Say I need a 600px X 300 px image. A
regular scrapbooking document is 12" x 12" or 3600px X 3600 px. So I set
up this proportion (stay with me here! it's easy!). I wrote 600/300 as a
fraction and 3600/x to show the width as 3600 but I need to know what
the height should be.
you can see, to solve this proportion, I multiply the numbers that were
diagonal from each other, so 600 times the x and 300 times the 3600.
Then to solve for x, I divided both sides by 600. This tells me I can
start with a 3600 x 1800 document. Then, when you finish making it,
resize the image to 600x300 and it will stay proportional! These
dimensions might be easily done mentally but you'll often get different
dimensions out there but you can use this to find out what it should be!
And if you get a little confused with the numbers, shoot me an email or
post on FB and I can help you with the math! ;) I am a math tutor as
well as a designer!