I don't think I have perfected it, but it has been working for me: Keep in mind, I am usually starting dynasties with 3* or worse teams, so not much experience with recruiting with more dominant teams.
Let's say I have 8-10 guys who have me as their NO. 1 team. If I have 450 recruiting points total, I will only add the amount of guys which allows me to spend 50 points on them week one. (This is after I've already offered them scholarship 5 points when I am setting up my board.)
In this scenario, maybe I have left off 4 guys who have me as their top school. To me, that is ok. If they are not on my list and with no scholarship offer, they USUALLY still keep me as their no. 1. I have no science to prove this, but adding a recruit to your list makes them wanted more by other schools.
Moving on: those initial recruits that I have added and spent 50 points on, they USUALLY sign with me. Maybe 1-2 don't, it really depends on their rating. 1-2 stars are obviously easier to get than 3-5 stars.
Once more points become available, I will spend those on the other recruits who still have me listed as their top school. You'd be surprised at how quickly your class can fill up just by doing this. Also, some guys will add you later in the season and make you their top school.
When you are late in the season, be sure to see which recruits are still available. The ones who have not signed are way more likely to sign with you, especially when you throw 50 points their way in week 11. Again, not always a sure thing, but it does work.
If you are a crappy school, sign whoever you can. Doesn't matter if they are a bust or not IMO. You just need bodies. A "bust" 4* at Akron/Buffalo/etc etc is better than a 1 or 2-star IMO. These "busts" are usually the guys who are available later in the season. Especially the higher-rated ones.
The postseason portal is kind of the same thing: Find recruits you want/need and give them 50 (or whatever max points you can give them) points as soon as you can. Those initial recruits are likely to sign with you.
Again, I don't think this is a fool-proof plan, but it has worked for me.