If you do this, the eye contact will take care of itself. Have respect for the Assembly, remembering that you are conveying God's Word to God's people in God's presence. If your height and eye-tracking abilities allow, hold the book while you speak to provide a visual reminder of the source of the words. This is good but not essential. Whether you hold it or rest it on the ambo as you read, you may find it useful to run your finger along the text as you read so you can freely maintain eye contact with the assembly without the risk of loosing your place.
Hand gestures are occasionally appropriate.
But use them only if they clearly enhance the reading. Avoid all gestures that do not actually help honestly communicate the reading. The operative word here is honesty. The lector obviously must be heard to be effective. To be heard by all in the assembly, you must understand the acoustics and public address system in your church.