Head strikes are a relatively common problem with inkjet printers and fine art media - the visible result can be smudging or smearing of ink on the page, marks around the edges of your prints, or ink droplet marks anywhere on your print.
There are several things you can do to reduce or eliminate these issues:
One way to set the platen gap is through your printer driver. You can save the setting as a preset for the media you are using so you don't have to remember to do this each time. Check your printer's manual on how to do this - sometimes it is just labelled as 'Use Thick Media' but often you have to go into 'Paper Configuration' and set the Platen Gap control to 'Wider' or 'Widest'. Below you can see an example from an Epson 3800 - this control is present in almost all Epson drivers in one form or another.
You can also generally set the platen gap usually using the printer's control panel.
Always ensure that the media you are using is within specification for your printer. For information on paper handling, settings and specifications refer to the user's guide for your product.