Once cleared for the approach the correct procedure will be to dial in the published glideslope intercept alt and prepare the a/c for the APP. ie. Arm APP ect. You should begin a decent to the APP alt, time (distance) permitting.
Should you intercept the glideslope on the way down, no hassle. You can also manage that decent using a reduced verticle speed decent should you want to achieve a earlier glislope interception. The long and the short of it is that you will normally be below the glideslope when cleared for APP and ATC is aware of the verticle profile to follow.