If people cannot find the donate now button, they aren’t going to donate. The button should always be placed above the fold – the area the viewer will see without having to scroll on your website. With longer pages, multiple buttons strategically placed are worthy of consideration. Make your button large – large buttons that stand out are easier to find and usually get a higher response rate than smaller ones. Make sure your button uses specific language – “Donate Now” or “Give Now” are popular choices.http://www.causevox.com/blog/4-tips-for-getting-more-donations/
Make it fun for your user to go through content. Buttons that look like fun to click.
We made the buttons on the screen look so good you'll want to lick them.Steve Jobs
That's the last question you want crossing your Web visitor's mind, especially if they have arrived at your site through some sort of marketing offer. From the perspective of your visitor, it should be clear and obvious where they need to click on your landing page to get them closer to their goal. If your visitors have to spend time deciding where to look and what to do, they'll most likely get frustrated and leave your site in search of more effortless experiences.
Handy info from, http://www.clickz.com/clickz/column/1936048/obvious-action