In C#, if 2 processes are reading and writing to the same file, what is the best way to avoid process locking exceptions?

using (FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.None))
{
    using (TextReader tr = new StreamReader(fileStream))
    {
    	string fileContents = tr.ReadToEnd();
    }
}

using (TextWriter tw = new StreamWriter(fileName))
{
    tw.Write(fileContents);
    tw.Close();
}

using (FileStream stream = new FileStream(@"C:Myfile.txt", FileMode.Open, FileAccess.ReadWrite, FileShare.Read))
{
   // Do your writing here.
}

using (FileStream stream = new FileStream(@"C:Myfile.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
   // Does reading  here.
}

using (FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
{
    using (TextReader tr = new StreamReader(fileStream))
    {
        string fileContents = tr.ReadToEnd();
    }
}

FileStream fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write, FileShare.None);
using (TextWriter tw = new StreamWriter(fileStream))
{
    tw.Write(fileContents);
    tw.Close();
}

if (!info.Exists)
            return 0;

        return (double)info.Length;
    }