Properly constructed garden steps are more than a convenience. The also may serve as a retaining wall, holding back soil erosion. This means you need to plan carefully, and securely anchor them into the slope they ascend.
Decide how many steps you will need, how deep each horizontal tread will be, and how high to make each vertical riser. Here's a useful rule: The tread dimension plus the riser dimension should equal about 17 inches. Try to make your riser dimension no more than 7 inches and no less than 4 inches. No matter how you juggle the figures, just be sure all treads and risers will be exactly the same depth and height: Changes break a person's stride and cause stumbles.
Also, be sure to take into account the depth of tread-finishing materials and mortar, if any, when planning a concrete foundation.
Use stakes and a level string or board to determine the total rise your steps will ascend and the total run they will traverse. To determine how many steps you will need, divide these measurements by combinations of tread and riser sizes until you come out with equal-size steps.
A caution: Building codes usually place limits on tread and riser sizes and other stairway dimensions, so check with local authorities before finalizing your plans. Codes also mandate handrails in some situations.
1. Excavate slope. Cut carefully into the slope, making room for the desired tread and riser dimensions. Steps of two 8-inch timbers work well if they overlap by 4 inches. Lay the timbers, pound into place with a sledge, and check for level.
2. Add timbers and secure. Using an electrician's extension bit, bore holes at the front edge of each timber into the one below it, then pound in rerod to tie them together. Also bore horizontal holes to secure each timber to the one behind it.