Sir Mix-a-Lot liked big butts, but I prefer big buttons. Your email buttons are the clearest and simplest way to tell someone to ‘click here’. Here are some tips for your buttons:
Keep the copy short, up to around 5 words MAX, and either take the position of the button or the reader. For the button you can use something like ‘click me’, and for the reader, you can use ‘I want it’ or ‘Give it to me’. Also, make the text bold, so the text really stands out.
Make your buttons FAT. Add some lovely padding around the text and make the button pop. Try to keep the button to a fixed width (with the exception of mobiles), so the button looks like a button. We’ve seen buttons that are full width and have no radius, so the ‘button’ just looks like a heading instead.
You can google about the psychology of colour, there’s a lot written about it online, but bright colours work best, like a bold green, blue or red colour.
Try to position your button towards the top of the email, and centralise it. You can also add a button to the main banner graphic (called the hero image), to let the reader know that the banner is also a link.