Or you can simply gather up a couple household items. What you need is a plastic bucket (unless you're willing to clean your clubs in a bathroom or kitchen sink), a mild dishwashing detergent, an old toothbrush or other brush with plastic bristles, and an old towel for drying.
Step 1: Create Suds
You only need enough water in the bucket to cover the heads of your irons.
Step 2: Place Irons in the bucket*
Set the bucket down, then place your irons in the bucket with the clubheads submerged. Notice how the clubs' ferrules are above the level of the water and suds.
Allow the irons to soak in the warm water for just a couple minutes. This will help loosen dirt in the grooves of the clubface, and allow the suds to begin working on oils and golf course chemicals that are on the clubheads.
*you can also place your wedges in the bucket too, no putters or drivers (those usually don't get dirty anyway, i'll talk about woods/hybrids later)