public class App : Application
{
    public override void OnCreate()
    {
        base.OnCreate();

        string libraryPath = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
        string sqliteFilename = "db.db3";

        string path = Path.Combine(libraryPath, sqliteFilename);
        conn = new SQLiteConnection(path);
    }
}

public class Database
{
    readonly object locker = new object();
    SQLiteConnection database;

    public Database(SQLiteConnection conn)
    {
        database = conn;

        database.CreateTable<Tabla1>();
        database.CreateTable<Tabla2>();
    }

    public IEnumerable<Tabla1> GetDatos()
    {
        lock (locker)
        {
            return (from i in database.Table<Tabla1>()
                    orderby i.Titulo ascending
                    select i).ToList();
        }
    }

    //Etcétera.
}