I'll fire a few of my observations from my current Germany 1941 start long campaign:
1: Try spotter planes, and scouts. Look for smoke collections later. Advance key front units one hex at a time and turn to look several times each (yes it is tedious, but can help).
2: I have gotten local superiority on assaults, advances and meeting engagements by "loading" my deployment to north or south with approx. 70-75% of my forces, and use a detachment to screen the other side. I also will protect a flank with smoke. Especially on assaults. I have rolled up the south flank and wheeled north on a few battles much more effectively than I would have thought.
3: On LOS, remember that the computer can check 1000's of LOS's as a calculation where we have to do each one per unit manually. My AI seems to place a lot of units IN my LOS or range freqently. It still advances too recklessly in many meeting engagements.
4: Maybe I am lucky, but my casualties hav been relatively low, in that I am not using my whole point allotment each time just to rebuild. I actually had points to buy some mobile AA in my third battle to expand my core.
I have found AI artillery to be quite worthy and it causes many losses. I am developing a style of creeping advances in 2-3 turn spurts. Let the AI see some units collect. Move while they are in the 2 turn delay for artillery plotting reaction time. I think the AI ini WinSPWW2 is better than WinSPmbt which was better than SPWAW which was better than all the DOS SP versions. Currently, artillery seems tough and fair (although my 1941 opponents due stack up big battery/mortar numbers). Infantry in defense, and ATGs seem 'above average'. Luckily, the Soviet commissar likes charging his T-26s and BT-2s across the field of fire for my III-h's.