Wht to do if I was just charged with alcohol intoxication and criminal trespassing 3rd degree?

For a first offense, you are looking at a probated or lower level jail sentence.  Jail time ranges from 48 hours to 30 days in a county jail.  Probation periods can last a few months, usually a year or two.  While on probation, you could be ordered to complete community service hours, pay a fine, a pay court costs.  Depending on your blood alcohol level, all of these ranges and sentences ranges could increase. 

Even though the sentencing range doesn't seem that severe, a DWI conviction have some serious short and long-term consequences, especially considering how young your are.  The first immediate result is that it could also result in a suspension of your driver's license (impairing your ability to get to work or school).  The second potential consequence is higher insurance premiums.  DWI's also tend to haunt people in their career choices.... some employers and licensing agencies do not allow persons with DWI's on their record to be considered for a job or a particular field.  Even when it's not a felony DWI, some countries do not allow persons with a DWI to enter their country.

The long-term consequences tend to hurt people more than the initial sentence.  If you can hire an attorney, you should.  Any attorney can give you an assessment on the strength of the case against, and possibly help you beat the case with a valid legal defense.  If the evidence is fairly strong against you, then they may be able to help you bargain for a different type of sentence or charge-- so as to avoid many of the negative consequences associated with a DUI conviction.