Importing to Photoshop from Illustrator or InDesign
Designing the creative is very often done in Adobe Photoshop, which is why we use a layered Photoshop .psd file format as the starting point in creating responsive ads.
However if you're using either Adobe Illustrator or Adobe InDesign to design your creative you need to first import your creative to Photoshop.
In Illustrator you can just select all the paths of a specific element and copy+paste into photoshop. In photoshop you can choose to import the paths either as Pixels or Smart Object. If you import as Smart Object you need to also rasterize the layer before uploading the .psd to ResponsiveAds.
Repeat this with all elements until you have each element as a separate layer in Photoshop, then save and upload to ResponsiveAds.
In InDesign you can use a handy Applescript to automatically convert your InDesign page to Photoshop layers. You can download the Applescript from here
How to structure layers
When you upload the .psd file to ResponsiveAds, each photoshop layer is converted to a separate element. The best advice to structuring layers is just "Keep it simple".
You should merge all the separate layers that make up a single visual element, because then you don't have to move and resize multiple different layers in ResponsiveAds. The fewer layers you have the more simple it is to configure the different layouts.
However if you realize that you should have separated an element into two different layers you can always save those elements separately later and upload them in the editor (just remember to delete the old element to prevent unnecessary weight in the ad and loss of performance)
Dealing with elements that span outside of the Photoshop canvas
Layers in photoshop might have content outside of the Photoshop canvas and when you upload the .psd to ResponsiveAds the whole layer gets converted to an element.
This is very handy when you have an element, like a woman's face, that you want to only show half in one size, but the whole face in an other size. However, in Photoshop, it's sometimes easy to forget that a layer has content outside of the canvas (you can see the whole layer content with CMD+t/CTRL+t) and if the whole layer is massive in size and you're only using the visible part, it will bring unnecessary weight to the ad and loss of performance.
In these cases you should crop the layer by copy+pasting the visible part of the layer into a new layer and then deleting the old huge layer.