We have any easy, fun, organic way of making simple app mockups. We've designed an entire template for these mockups that we call ADPs (App Design Packages), which is already full of PNG elements (like buttons, icons, etc). It's designed to perfectly match the basic types of mobile app features we offer (which you'll notice and become familiar with almost instantly).
Mostly, what you'll be doing is switching/swapping out background images, logos, adding different accent colors based on each client, etc.
We will provide you with a list of potential customer/client leads/targets that usually may include some website or company info - and your job is to quickly glance at their website, content, logos, colors, etc. to get a "feel" for their "brand". Then, you'll use some or all of those elements to create your ADPs (ie. mockups) so the designs are really relevant to the client's brand, business, idea, organization or company.
An ADP typically consists of 10 PNG elements:
App Icon -1024 x 1024px
Splash page - 768 x 1366px
4 Slide pages/screens (slide template) - 768 x 1366px
About page (content page template) - 768 x 1366px
Services page (content page template) - 768 x 1366px
Contact page (content page template) - 768 x 1366px
My Website page (webview page) - 768 x 1366px
Note: Try to do these in PNGs at 300 dpi (ie. resolution)
The My Website page is basically a screenshot of the client's website in a responsive size (ie. what it would look like on a phone). You can do this easily by adjusting your browser to be a similar size of an average cell phone or you can just actually pull their website up on your own phone then screenshot it and email it to yourself.
ADPs are meant to be nice and quick marketing tools - our little way of saying "hello" to potential clients. They really get people's attention and make people take us seriously. Because our templates are very UI (User Interface) driven and already have all the elements in place, it's usually quite easy and fast to swap graphical elements out for each new client's ADP (for example, you'll probably only need to add 1) a logo, 2) background image, 3) some text for the slide text and 4) some button text to the Slide Templates to make each slide - so 4 changes per slide). We typically like you to spend no more than about 20 minutes on each ADP set. So as long as you average 3 per hour then that'd be great.