Purchase tickets for the Monster Ball concert in your city as far in advance as possible to maximize your chances of getting a close ticket if the concert you attend is seated. If your seat is close in the first place, it isn't necessary to engage in stage rushing or other tactics to get a close glimpse of Lady Gaga as she performs.
Listen to local radio stations that play Lady Gaga's music in the days and weeks leading up to the concert to see if any give away front-row tickets or meetings with Lady Gaga. Artists such as Lady Gaga give away a certain amount of tickets per concert to radio stations as a means of promotion.
Speak with a venue security person when you arrive at the concert, regardless of where you're sitting. Ask if there is any portion of the show when it's appropriate to walk up to the stage. Some venues, for example, permit "stage rushing" during the "encore" portion of the show after the main set. If you do stage rush, use caution not to get hurt or injure anyone else, while making your way to the front of the stage as quickly and directly as possible.
Arrive as early as possible at the venue if the concert is general admission. General admission means that seats aren't assigned, so the first people in the venue are closest to the stage. Contact the venue in advance of the concert to ask whether sleeping outside is available if you feel you need to camp overnight to get a good spot.