I have plant to cut plasmid using double digestion (SmaI and KpnI). These two enzymes are different about the condition. The suggestion is sequential digestion. Any advice?
Firstly check for their compatible buffers, which is normally available on the manufacturer's website (NEB, Fermentas, Takara whichever company's enzymes you are using). If you can find such buffer in which both these enzymes shoe 100% activity, then you can easily go for double digestion and there won't be any need for sequential digestion.
Navjyoti is right, but if there is no common buffer, it is not a lot of effort to first digest with SmaI, do a quick agarose gel to check for digestion, then ethanol precipitate and set up the second digest with KpnI.