It isn’t difficult if you take into consideration piazza del Popolo or piazza di Spagna as points of reference. For example, if you start from piazza del Popolo, having your back to Porta del Popolo, you’ll see three main streets ahead: just take the street on the right (via di Ripetta) and walk less than 10 minutes along that street. You’ll find the museum on your right (you’ll recognize the wall of the Res Gestae).

Hope this helps.

MR