The choice of the first sketch plane sets a quiet tone that has implications for the rest of your CAD model. It establishes the orientation of your part, which dimensions will be easiest to locate, and where future features will likely line up with the origin and primary axes. A bad choice might not even prevent the model from functioning, but it can turn every subsequent task into something much more complex than it should be.
Start with a careful study of the reference drawing, and pick out the view that conveys the design of the part most effectively. For a planar mounting bracket, the front view is likely to show the outline, holes and central slot simultaneously. For a circular knob, it may be the side view that presents a profile that you can rotate about a central axis. For a long rail or spacer, the end view might display a cross section that you can extrude out to a desired length. You want to pick a plane that shows the most salient features in as few separate operations as possible.
You also need to think about how the final part will be aligned to the front/top/right views. Centering and placing a centerline/axis on a face that is intended to align with the front origin whenever possible, so that subsequent mirrors, pattern features, dimensions and constraints have a reliable starting point. While a model can always be rotated after completion, realigning the internal feature order once you’ve got a set of cuts, holes, fillets and sketch-based features already in the feature tree can be painful.
To test this, try modeling the same small part two different ways. Make a simple L-shaped angle bracket with two mounting holes. Create the first iteration by drawing the bracket edge profile and extruding its width. The second would be to draw the face outline and then create the bent edges using additional operations. Note which version has fewer sketches and dimensions; how easy it is to position the holes; and what happens when you try to change the height or length of the bracket. Typically, the better sketch plane is the one that keeps the most basic dimensions readily available and minimizes the number of dependent operations.
Beginners often pick the sketch plane that looks the most impressive on a reference, rather than the view that is most descriptive of the actual 2D geometry. Perspective drawings help you understand the 3D shape of something but often obscure true-length dimensions and angles. Orthographic views are much more straightforward because they show width/height and width/depth simultaneously. When you’re working off of photos, try to picture front and side elevations (2D silhouettes) to help you understand how the parts should line up in your sketch plane selection.
It is possible to test a sketch plane before committing to it, by making only the initial profile and an extrude or revolution, and inspecting the final solid from the front/top/right views. The part should line up to the appropriate direction, any symmetries should fall on the primary axes, and the next primary feature should have a good location to be sketched on. If your holes, slots or mirror shapes already look awkwardly placed, you need to go back to square one while the model is still simple. A good sketch plane makes subsequent work seem like a natural extension, instead of a series of fixes and patches.