Small Aircraft; Low Wing; 1 Eng; Fixed Gear
Flight Crew Private; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 30; Flight Crew Total 680; Flight Crew Type 365
Confusion; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Environment - Non Weather Related; Human Factors; Procedure
While flying at an altitude of 3;000 feet; ATC assigned new altitude of 2;500 feet. I mistakenly entered 2;000 feet in my autopilot.  Once leveling out at 2;000 feet ATC informed me of my error and reassigned existing altitude (2;000 feet) as my new altitude.I believe this occurred due to a heightened work load environment I was experiencing at the time; rapid fire instructions being given by Controller within his busy airspace; and my reduced flight proficiency due to fewer hours flown over the prior several months.  I plan on making a concerted effort to fly at a minimum of once per week to maintain suitable level of proficiency.
GA pilot reported an altitude excursion and cited lack of flying as a contributing factor.