Ihsan (The Perfection of Faith) is worshiping Allah with perfect concentration as if you are seeing Him and if you don’t see Him, believe that He is seeing you.
To worship Him as if you are seeing Him can be attained by deeply believing in Him, His presence and believing that His existence alone is the real and ever- lasting existence and the origin of all existence. While being humble, lowly, fearful and by aspiring for His vision with an ardent love for Him. The love should absorb him so much that his "self " is negated.
If one does not behold Him in worship, one should persist in excellence of performance by believing that he is being watched by Allah the Most High.