Tuning the strings tends to pull it forward. Check its position frequently. If neglected, the bridge may warp, even break. If it requires adjusting, grasp the bridge at both upper corners with the thumb and first fingers of each hand while holding the instrument firmly braced. Then gently move the top of the bridge to a perpendicular position or ask your instructor or local shop for help.
Old strings are lifeless, false and dull sounding.
Replace them with good fresh strings. The finest instrument cannot sound its best with poor strings. Put new strings on one at a time. Guard against the bridge being pulled forward while tuning new strings up to pitch. This can seriously bruise the wood.