STEP BY STEP / Grab a brush
1 Make a brush
Go to File> New, choose A4, set Background Contents: Transparent, hit OK. Grab the Elliptical Marquee tool. Shift-draw a small circle, go to Edit> Fill and use black. In the Layers panel, set Fill 50%, then go to Layer> Layer Style> Stroke. Set Size 8px, colour black. Hit OK.
2 Define a brush
Go to Edit> Define Brush Preset. Name it and hit OK. Create a new layer, hit Alt+Delete to fill it, go to Layer> Layer Style> Gradient Overlay. Click the preview bar, double-click the little squares under the gradient to choose two colours (blue and purple here). Hit OK.
3 Customise the brush
Grab the Brush tool. Toggle the Brush panel in the Options bar. Use Brush Tip Shape, set Spacing 100%. Use Shape Dynamics, set Size Jitter to 100, Minimum Diameter 50. Use Scattering, set Scatter 1000, Count 3. Go to Transfer, set Opacity Jitter and Flow Jitter to 50%.
4 Paint and blur
Make a new layer, click the Blending Mode drop-down in the Layers panel, choose Color Dodge. Pick a light grey and paint scattered bubbles. Pick Filter> Blur > Gaussian Blur. Blur the bubbles (Radius 40px), hit OK. Repeat on another layer, with a lower amount of blur.
5 Build it up
Continue painting and blurring on more layers (set to Color Dodge), varying the brush size and blur. Go to File> Place Embedded and open the bokeh_cutout.png start file to drop in the subject. Add more bokeh layers on top. Hit Ctrl/Cmd+Shift+Alt+E to merge a layer.
6 Add tonal effects
Select Filter>Blur Gallery>Iris Blur and blur the edges of the frame. Go to Filter>Camera Raw Filter. Grab the Radial Filter, set Exposure -3 and drag to darken the corners. Create an adjustment layer, choose Colour Lookup and select a tonal preset, like ‘2 Strip’ here.