Applying a thin coat render isn’t too difficult if you are competent with a trowel. Apply your base coat (with mesh reinforcement) and ensure it is flat and uniform. There should be no trowel marks on the surface and the thickness should be consistent. Apply a coat of primer once the base coat has dried. (About 1 day per mm of base coat thickness.) Once the primer is dry, normally about a day, take your tub of top coat render and ensure it is properly mixed and prepared. Apply the render using a steel trowel to a thickness about twice that of the aggregate size. For a 1.5mm render this will be put on at between 2.0 and 3.0mm thick. Flatten the render with your trowel until the first set is achieved. The render will skin over once the curing starts and it is important to remove the excess render and to texture it before this starts.  Now go back over the render with an acrylic trowel and remove any excess render. This will flatten the render and reduce the thickness to just more the the aggregate size. For a 1.5mm render this will end up between 1.5mm and 2.0mm thick. Make sure there are no drips or trowel marks on the render. To remove them, float the area again with your acrylic trowel. Do not apply the top coat render to a wet base coat. The moisture will get trapped there and will try and migrate through the render after it is cured. This will lead to render bubbles and future issues.