Prior convictions may be used against you if they are related or similar to the current charges against you.  Proximity in time is another factor to consider with regard to the use of prior convictions.  If prior convictions occurred many years ago, the judge may exclude them as being too prejudicial in the current case.  If your attorney brings up the issue of prior convictions in court, the prosecution can then proceed with that issue.  The prosecution cannot open the door (raise that issue) without it having been initially raised by your defense attorney.