Lets start with the petals of the rose: A simple plane. Add some "Loop Cut and Slide" to subdivide the plane, then give it the shape of one petal. This one has to be duplicated and rotated a few times, until the rose's head looks good to you.

The leaf is a simple Bezier-Circle, modified to get the shape of a leaf.

The stem is an Bezier-Curve with an Bezier-Circle set as "Bevel object"

Here's the whole scene so far:

I added another plane with procedural Wave texture which I used as background (to fill a bit the dark area in the background, but this is optional...

The bokeh-look:

This one is fun: Add a plane, and extrude with boolean-operation the shape you like (can be a star, or like here, a heart). Place this plane very close to the camera's objective (you'll maybe have to play a bit around). Don't forget to center the hole in the plane with the camera's objective. Turn the Depth of Field radius to at least 0.15, otherwise the effect won't be visible. Put some light emitting objects (a sphere) very far behind the object, and set the focus either on the main object or an Empty-object, to get the blurry background.