I dive headfirst.
You ought to test the waters. Put your toe in, see how it feels. Imagine how it would feel over your whole body, that sensation that your toe just felt. Take into account that the sole of your foot is less sensitive than your skin. Think about how long you should wait before jumping in. Maybe even sit for a while just dangling your legs in the water, and wait. Wait even though you’re reasonably sure you’re good to go. Don’t let yourself be swayed by how great your feet feel, how cool, how relaxed. Don’t jump in yet. Take your time, be careful, thorough. And slip in finally, slowly, after ages of deliberation and consideration.
But I dive headfirst.