Do you have an ironing board?
If not - then I sometimes iron on a slightly damp towel on a kitchen surface.
Really take note of the ironing instructions on the garment (one dot = cool iron, two dots = warm iron, three dots = hot iron).
If the garment is a man made fabric, or shiny, or silky fabric, then I tend not to use steam/water in the iron - because I don't want water marks.
Always make sure the 'foot' (ironing part) of the iron is clean, especially when it's new, give it a good wipe with a damp cloth before using. Then test it on something you don't care about (like a tea towel) before ironing your clothes.
Test the iron on a small and inconspicuous area of the clothing, to make sure it doesn't leave a mark or change the texture of the fabric.
Don't leave the iron on the fabric too long, keep moving.
The iron will stay hot for longer than you think so mind you don't burn yourself when you've finished.
If you have an ironing board, all the better - because that means you can post the ironing board into the garment, so you're only ironing one 'ply' of fabric at a time.