There are many strategies you can use to grow microgreens like planting 1 tray each day or 4 trays every 4 days. Some varieties take more than 8 days to grow so you will need to adjust for that. If you want a constant supply you need to plant a new tray every time you harvest a tray.
My favorite schedule is to plant/harvest 2 trays every other day. This lets me have a couple different freshly harvested varieties on hand ready to use. For me this is the best option as the microgreens are either cut that day or maybe one or two days old which is still very fresh as microgreens can stay in the fridge up to 12 days.
One option is to plant/harvest 1 tray every day. With this option you can cut your microgreens almost everyday at the dinner table. You can't get any fresher than that!
Another option is to plant/harvest 4 trays every 4 days. This option is great in preparation for a party as you will have plenty of microgreens harvest all at once.
There really is no best way to harvest. It really is up to you as to how and when you want to harvest your microgreens.