sreesha I am getting 0.7" to 1.5" guiding error, which I am not happy with.
What do you mean by "not happy with?" Is it because of real technical reasons, or because of some OCD reason, or some old wives' tales?
Bear in mind that if you are not on Mauna Kea or Paranal, your stars will be bloated by atmospheric turbulence ("seeing") to something between 2" and 3" on a decent night! You might get slightly below 2" on an exceptional night, and worse on a poor night.
That, together with the Airy size of your OTA, are going to make a guiding error of 1" virtually not visible.
Assuming all the factors are independent (no reason to think they are not), then variances add, and the star size would be sqrt( A2 + B2) for the case you guiding is absolutely perfect (zero RMS error), versus sqrt(A2 + B2 + C2) for the autoguided case.
A is the Airy size (it will depend on f number). B is the atmospheric turbulence, and C is the autoguiding error.
So, let A be 2", and B be 3" for an average night, and C be the 1" RMS that you measured.
We get sqrt( 13 ) for perfect autoguiding, and sqrt( 14 ) for your 1" guiding.
Imperfect focusing will be much worse than that! In fact, I challenge you to see the difference between a star with a diameter of 3.6" and a star with diameter of 3.75".
I took many images (with versions of ASIAIR autoguiding that were completely fubar) with 1.5" RMS guiding error, and they were fine.
Chen