The one-handed American manual alphabet is generally used to fingerspell names, street names, places, restaurants – things that don’t quite have a sign. Try avoid fingerspelling every single thing – focus on learning what the signs are and/or gesturing to get the point across.
When fingerspelling, try to keep your hand fairly still. Avoid bouncing or stamping your letters. To practice this, you can rest your elbow on a table and try to fingerspell words without your elbow moving off the table.