Have the elders "invited" you to a JUDICIAL COMMITTEE (3 elders) or to meet with 2 Elders (investigative committee)?
IF they have already formed a "Judicial Committee" then they believe they already have the "evidence" to DF you. That would mean TWO eye witnesses or strong circumstantial evidence (ie you stayed overnight alone at the home of a lover). The 2 eye witnesses can be testifying to two different events (ie you spoke apostate ideas to both persons at different occasions; or 2 people saw you smoking at two different times).
If you are to meet only with TWO Elders, then they are still trying to "get the goods on you", hoping really for your "confession" or that you admit to the "sin". In this situation, you can DENY DENY DENY. Frankly, most elders will follow those rules -- with only ONE witness against you -- they'll drop the charges (and wait......). Or they'll hope you will answer the "apostate question": Do you believe the GB is the Spirit Directed channel used by Joe Hoover to direct the Flock?" (or something similar). If you say no or challenge that, then you have agreed that "you are no longer on of JW's".
If you are to meet with THREE Elders and you refuse to meet, they will DF you in absentia and call you (with two elders on the phone) to give you the results. The only way to avoid DFing is to meet with them and convince them the two witnesses are in error or lying, or to grovel for forgiveness and hope they find you "repentant". If you haven't been going to meetings, etc, then you do not "have the fruits" that prove you are repentant.
Good luck!