Here’s a page where the steps are outlined in the first two points
Also make sure your artwork runs slightly over what will be the finished cropped edge, to avoid a thin white band between image and the edge of the page.
Whether or not you have margins probably depends on the style of portfolio you want it to be. Personally I leave them off and place images to edge. If you do this use the crop marks and bleed setting when publishing from indesign. Then print on an oversize a4 and crop it down, this should avoid the printer cutting of the edges of your work.
I went looking for the same thing a while back and found this
I found it good and straight forward considering my limited knowledge of photoshop at the time although it will take alot of tweaking and practice to produce the quality shown in the posts previous to this!…[Read more]