I get out of bed right away. I’ve placed my alarm clock at the other side of the room and I sleep in an elevated bed, so once I’ve turned off the alarm, I can’t just trivially climb back into my bed, even when I haven’t slept enough.
(I use a Lexon Flip Mini and I’m satisfied with both the noise it makes and the way it works. There’s no way I would trust my phone with that task. I set phone alarms for many other things, that said.)
After I’m up, I immediately go to the bathroom and go through a whole routine (centered on showering), which I trained myself to always do in the same order so I wouldn’t have to think about it. After that, I dress in the clothes I’d laid out the evening before, I go back into my room (which contains both my bed and a tiny kitchen), eat, and put food and water/tea for the day into my bag.
On my days off, if I’m not feeling too tired and discouraged, I go for a run just after turning off my alarm and go through the bathroom routine just after coming back.
Like many people in the comments, I typically wake up just before the alarm — unless I haven’t slept enough for a few days, which used to be a rare occurence but happens way too often nowadays.