Tell your child that they are going to help gather items found in nature.
Give them a tray, bucket, bag or something that they can put in the items collected.
Encourage them to look for many different types of items outside that they would be able to cut.
Once you have several items (8-12 minimum) allow your child to practice with scissors and cut these items up.
This will build fine motor strength as well as build on their skills to be able to cut and hold scissors properly and safely.
Extension:
Talk to your child about scissor safety.
When are they allowed to use scissors?
Where are the scissors stored? Can your child easily access them without help? (You may want to consider storing all scissors in a safe secure location to avoid any accidental cutting).
Asking permission prior to cutting
Holding scissors properly
How to safely walk with scissors
Never run with scissors
Continue to allow your child opportunities to practice cutting. The more they use them, the better they will be at using them properly and build all those muscles.