Yep, first check to make sure you have all the fabric required. Read the instructions carefully to see if the sashing is to be cut first from the yardage, if it has sashing. Is it a sampler or a repeated block? If it's a repeated block, read the cutting instructions carefully and cut and sew your first block. If it works out well and measures what it is supposed to continue on. If it's a little small or big, that won't matter with a repeated block. If the blocks are all different they do have to measure the same for ease in assembly.
Remember if you goof up, it can become a couch throw instead of a bed quilt. We all started as beginners and had to learn by trial and error (lots of error in my case) Now there are wonderful resources for new quilters either on the net or here at QB. Have fun!