Some artists may be able to map out a complete design in their heads or make it up as they go. I've tried this and I have only rarely ever loved the results. Most of the time I need to trial and error and draw it out to be satisfied.  

When you're just starting out, I do recommend beading without a pattern, just practicing the stitches and adding different colors, opacities and finishes of beads. It's a great exercise for learning what looks good together and how the design comes together bead by bead. You can always snip it apart and use those beads for another project! 

There are many ways to draw out your bead designs, from standard graph paper to drawing programs for tablets and even specially designed graph paper, both print and digital. I've treid several and one of my favorites is this Two Drop Brick Stich graph paper from beadshop.com

Get it for free here:  https://www.beadshop.com/pages/two-drop-brick-stitch-graph