If you must close the gap (diastema), the least invasive/expensive would be to place bonding between them. More expensive options include veneers if your existing front teeth are solid or clear liners/braces to move teeth (which takes time). If it were my teeth, I would leave it alone since I don't like any of those options (I don't want any drilling, bondings & veneers coming off or trauma to my teeth and I'm less vain).