There are two options I've found that work.
The easier one is, just controlling the flow. Make sure the front bottom edge of your measuring cup is also above the pan, and while it drips - it will drip into the pan. This can be tricky if the pan is only a little wider than the measuring cup itself, but it can often help once the dripping starts (since once the front is wet, there's a bit of pull that way via surface tension, and the liquid likes to keep following that path). Specifically, in that picture, the measuring cup can probably be moved two or three inches towards the far side of the pan without issue, and the drip is only one inch or so from being over the edge of the near side.
The trickier one is to pour more cleanly. Pouring fast helps - one sort of example is quickly dumping it into the pot, where there isn't time to drip and the sprout is very quickly lower then the bottom edge anyway... though that does mean you have less control over the flow. But, more than that, the trick is to never "let up" - that is, once it starts pouring, the angle should only get deeper, never shallower.
When the angle gets moved from deeper to more level, even a bit, the spout functionally swings backwards in relation to the pot, and the angle of the stream of liquid can easily sloshes back enough to touch the side. Once wet that side becomes a path of less resistance, and so it slides down instead of pours clean. It is really easy to do accidentally, a little rock backwards to slow the stream or gentle it as the pot gets fuller, or to look into the pot or away to something else, or just any means of getting distracted for a second.
As an aside, if it starts to spill down the side when pouring, either move the bottom over the pot, dump the liquid fast, or stop to clean and dry before pouring again - the wet side is easier to go down, so once it starts it won't pour cleanly till the side is dry again, despite most any techniques.
Well, actually, another possibility is to nudge the spout of the measuring cup over the side of the pot, actually touching the pot's side. As I mentioned, running down a side is easier than jumping off - so if the spout is touching the side of the pot, it will tend to run straight down that inside instead of trying to jump over the edge backwards to run down at a shallower angle.