Most coasters are around 100mm in diameter so start by using the circle tool in XCS to create the outline.

If you are engraving onto ready made coaster this circle will just be used to help centre your design and should be set to score at 1% power, but if you're cutting the coasters from a larger piece of wood remember to set this layer to cut with the appropriate power settings for your machine. 

Next add a text box and type ‘Happy St Patrick’s Day' or do a quick google search and find some inspirational, interesting, or funny Irish quotes.

Then choose a nice font, a favourite of mine I often  use for engraving is called ‘Dancing Script’ and can be downloaded from Google Fonts here if you don't already have it installed.

Once you're happy with the layout of your text you might want to add some simple images to make your design stand out.

Google images will some good picture but creazilla.com is often better for laser engraving as the images are usually higher quality and sometimes available as SVG files.

Once you have chosen some images you can uses the editing tools in XCS to turn them black and white or remove the background if required.