Depends on your expected draft position and willingness to invest (they should be related).
Assuming you have a high draft position, I'd invest 50-70 points by doing the Group Demo, interview the 5 stars and then do a couple of random scouting in the other draftees and interview the 5 stars until you have enough good prospects for your position (so 3 if you pick 3rd, 2 if you pick 2nd etc).
If you pick first and there are multiple good prospects, you should use a skill showcase/practice drill to reveal key skills. For me, that would be OD (on ball defense) for a tall player or IS (post up dribble) / ID (Cut inside) for a short player, because those are hard to train so you want them high.
The draftees will only appear after ASB so you need to wait anyway, but you can scout as soon as they become available. If you need more points you can do most of your scouting and then decide if you want to spend more points at the end of the season.
I wouldn't use the Combine since the 19-year old draftees have been greatly improved and are worthwhile to scout too. In some older guides you might find the advice to use the Combine to find the 18-year olds and leave the 19-year olds, but that's not useful anymore if you ask me.