Match the marker to the paper
Water-based markers are forgiving but can roughen thin paper when layered heavily. Alcohol markers blend smoothly but bleed through more easily. Whichever type you use, place a scrap sheet underneath and make a small swatch card before coloring the page.
Fill in a consistent direction
Start at one edge and move across the region with a steady speed. Overlap strokes while the ink is wet, and finish a section before jumping to another. For broad areas, use the widest part of the tip; use the point only near corners and outlines.
Add depth with a second pass
Choose one side of the object as the shadow side and repeat a shorter pass there. Two related colors usually look cleaner than many competing shades. If streaks are the problem, the page on even marker fills has a more focused checklist.