Check the layout before you heat it
A missing bead is much easier to fix now than after ironing. Compare the board with the pattern, especially the eyes, narrow stems and joins between separate shapes. Taking a quick photo gives you a useful reference if the board gets bumped.
Work on a stable, heat-resistant surface. Keep the ironing step with an adult when children are making the pattern.
Use the instructions for your beads
Use the ironing paper, heat setting and method supplied for your bead brand and size. There is no single timing that suits every iron and bead series.
If you want to mix brands, make a small test piece first. Similar colors and diameters do not tell you how evenly the beads will fuse.
Let it cool, then check the joins
Follow the cooling instructions before lifting the piece from the board. Look closely at thin bridges, corners and keychain loops for loose beads.
If a section feels weak, return to the instructions for your beads before applying more heat. A thicker outline may be a better choice for a design that will be carried on a bag or keyring.