Multitasking has become such a default for me that when I do stop, drop and fully engage with one thing-- just one thing-- I feel like I have a superpower. It's the getting there that is the hard part.
1) Put your phone in a drawer. If you can't do that, before you lock your phone pull up an image that reminds you what you're up to-- or the Batman "Stop Procrastinating" meme...
2) Open up one tab at a time online.
3) Set a timer for how long you're going to work on a project. Focus solely on that-- no exceptions-- for the duration of the timer. When the timer goes off, take a little break, and then set again. Experiment to find the increments that work for you.
4) OR play the beat-the-timer game. The intention is not to rush, but to eliminate unnecessary dilly-dallying. Push the edge on how long you think a task will take so you’re forced to commit to the challenge! I use this for picking out outfits, picking out recipes, preparing acting sides, Internet research—any task that will inevitably drag on if left to my own devices.
5) Maintain a clean and orderly working/living environment to minimize distraction.
Finally, remember: You don't need to be or feel "busy" to be doing it right. Breathe, ground yourself, and uni-task and I promise you'll be more productive and produce higher quality work.