Take accurate measurements of the square table you intend to cover, using the measuring tape. Keep in mind, in order to assure your table as a prominent focal point, you want the plastic cover to fit nice and neat, without overhanging. Your measurements should not only account for length and width, but also thickness. Add two-inches plus the thickness measured to the width and length, to determine final measurements.
Bring your measurements along with you to the store to select a roll of plastic wide enough and long enough to compensate for your final measurements. You will want to purchase a roll of plastic that has some thickness and sturdiness for durability, but still retains a good degree of flexibility to fold without creasing. Be sure to purchase the eight metal table cover clips the size of your table thickness and some clear double-sided tape.
Cut the plastic with your scissors, using the t-square to ensure a straight, precise cut. Place the plastic you cut out on the table, center it and verify the accuracy of your measurements.
Fold edges around and underneath the thickness of the table and affix on the underside with double-sided tape. You will want to cut sections of the double-sided tape about one-inch in size and place then evenly when affixing edges on the underside.
Place your metal table cover clips and affix the two at a time in an "L" shape at the corner of each table, spacing the "L" the width of your table legs.