Read a lot of the posts here. Watch videos on YouTube. Make sure your surface is very clean before you spray. Use a good wax remover. You can get a bottle from the auto paint supplier. One bottle goes a long way.
I used a direct to metal primer. Then 2 coats of base. And two coats of clear. Follow the instruction on the cans of paint. Get an activator that matches the temps you will be painting in. Dont rush! Let the coats flash/dry between coats! Usually about 15 to 30 mins. Depending on the temp in your booth/garage. A tip I saw was to touch an area of overspray to see how tacky your last coat is. You don't want to spray the next coat if the one that's on there is still wet.
Is the bed liner a spray on or roll on? Either way you will get overspray on it unless you tape it off. Not sure if you care? But if you do and it's a roll on maybe do the liner last? Especially if it's a roll on. Less chance of getting it on your new paint job. If its a spray on I'd personally do that first. Then paint my car. Maybe someone with more personal experience can chime in. Best of luck!