Utility (functionality) aspect is the first principle of design method. So that, the reach the optimal untility aspect, the staircase should be designed according to the user needs. Making some lists of the user need can halp you to get that purpose. Here are some lists that you have to know before design your staircase:

• Who is the user of the staricase? Like everyone, children or old people which need a special aid tools
• What kind of things that will be brought while use the staircase? It will influence the width of the stairs design, so that easy for use
• How often the staircase will be used? It will influence to the location in the home layout. For example, staircase for service activity will be put on service area, such as kitchen, pantry or warehouse
• The angle of the staricase. Although, there are many design of staircase, but you have to put user-comfortablity factor as the first considerable. So, the normal staircase should be design with formula : 2a + b = 60-65 cm. ( a : height; b : width of ladder-step). The steep-staricase is a staircase which is 2a+b > 65cm, and the slope-staircase is a staircase which is 2a+b<60. In other way, It can be said that the height of ladder-step is 14cm-22cm, and the width of ladder-step is 20-33cm.
• The length of the staircase. The location of the staircase as a connection between two floors need to be counted very well, especially the dimension of staircase. There is formula that can be used for counting the length of your staircase : (H/t) X L = Length of Staircase (H : height between two floors;t : height of ladder-step; L : width of ladder-step)
• Design of balustrade/handrail. The strength of balustrade depend on the connection between balustrade and ladder-step. The comfortable balustrade have 80 - 100 cm heigth and 4-5 cm length for diameter.
• The lighting on the staircase. Last but not least, do not forget to put artificial light on the staircase.