How to make serialized data compact?

Question

i wrote an application which is a custom console that allows execution of various commands. One of the commands allows serialization of data. The input data is a string, which is a list of comma separated values.

My question is - how to make the serialized data compact as much as possible? The serialization format is not important for me.

Here is the command's code:

using CustomConsole.Common;
using System.IO;
using System.Xml.Serialization;
using System;

namespace Shell_Commander.Commands
{
    public class SerializeCommand : ICommand
    {
        private string _serializeCommandName = "serialize";
        public string Name { get { return this._serializeCommandName; } set { _serializeCommandName = value; } }

        public string Execute(string parameters)
        {
            try
            {
                var splittedParameters = parameters.Split(" ");
                var dataToSerialize = splittedParameters[0].Split(",");
                var pathTofile = splittedParameters[1].Replace(@"\", @"\\");

                XmlSerializer serializer = new XmlSerializer(dataToSerialize.GetType());
                using (StreamWriter writer = new StreamWriter(pathTofile))
                {
                    serializer.Serialize(writer, dataToSerialize);
                    var length = new FileInfo(pathTofile).Length;

                    Console.WriteLine($"Wrote file to: {pathTofile}");
                    return length.ToString();
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
                return "0";
            }
        }
    }
}

The command accepts 2 parameters:

1. Data to serialize
2. File path (in order to save the serialized data).

Example - for the "1,2,4" input, the following file will be saved:

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfString xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <string>1</string>
  <string>2</string>
  <string>4</string>
</ArrayOfString> 

EDIT:

1. I want my command to be able to serialize also complex objects in the future, so writing the string as is to the file is not a solution.

2. I want to use only standard serialization methods and formats.