Usually a good aim point while facing front on, is the lower front glacis (the lowest part of the hull) or any protrusions on the turret u can hit, or any little hatches u can see.
eg. here is the M4 Sherman weak spots http://wotguru.com/weak-spot-guide-m4-sherman/
or the KV-1 weak spots http://wotguru.com/weak-spots-guide-kv-1/
eg. here is the M4 Sherman weak spots http://wotguru.com/weak-spot-guide-m4-sherman/
or the KV-1 weak spots http://wotguru.com/weak-spots-guide-kv-1/