A quick basic walk-through for anyone having issues, and a question at the end.
I've done the special endings for all the girls that have them (I think the only one I haven't unlocked is Malice, and I haven't completed the one for Reisz), and if you follow set pattern it's actually pretty easy to get most of them and still have stats maxed or close enough to max that you still get a ridiculously good score (I was determined to buy back all my slaves but was kinda disappointed when I found out you couldn't for Rei). There are some variations depending on the girl and what ending I'm going for, but I usually do the following.
I usually pick male ponymaster (I usually only train one pony slave but having the skill start at lvl 3 is handy) with the onsen for the nice day to day personal income + more tiredness recovered from resting. Also, new gods, mostly for the chance to train Rei, otherwise I would go with old gods. That's just a personal preference, but I have noticed through some experimenting that some slave maker types/locations are ALLOT harder to go through the game with then others.
I usually use Shampoo for my assistant except for with Belldandy and refuse love requests. Rest when needed, and buy what you need at the shops as you can afford it. Ie. Bondage gear (only need to get it once), dildo, maid uniform, swimsuit (sometimes), 4k gold costume, everything at the salon that's permanent, and whatever is useful form the street vendor.
Rules:
All off at start, when obedience get's high turn on talk whenever and go out whenever to keep from taking conversation and joy hits. The exceptions to this are Kasumi who you need to allow to talk to her family and Rei who it won't let you turn off praying. Also you can't turn on speak whenever if your training the girl as a pony girl since they have to keep the bit gag in so you'll just have to deal with the -1 conversation per day.
The main point of the competitions is to bring in money. If you need it, go for whatever you think you can win. If not just skip em.
Day
Start off working at restaurant, accept when offered chef position, and continue until cooking is maxed.
Work at library until cleaning is maxed.
Do etiquette schooling until refinement is maxed, and by this point sensibility if your new gods or no gods (it'll make sense when you see the night plan).
Theology until morality is maxed (Max may be really low depending on the girl/ending you have set up. If blowjobs and fucking aren't maxed skip this and just keep doing restaurant/ending stuff)
If conversation still isn't maxed discuss until it is.
Then just keep working at the resturant until rep is maxed and make sure to give enough breaks/buy enough toys to get joy maxed. Do whatever after that.
Nite
As suggested before, have her masturbate until she's at 50 obedience (the exemption being Ayane which you have to spank until rebelliousness hits 0 first) then use dildo until obedience caps.
If it caps at less then 100 then spank twice and use dildo once a nite (don't do this combo more then once even if you can do six actions, it'll actually cause ob to go down most of the time if you do) and make sure she's getting enough rest. You don't want to start do or night with tiredness much above 50. This is CRITICAL to get some of the endings. Minako for example caps at 70, which is far to low to be lent out, but you HAVE to lend her out to get the cat savior ending.
When ob is at 100 do orgies until blowjob and fucking is maxed (possibly sensibility too), then strip until charisma and temperament are maxed. Both of these are useful sense they increase con, just be careful as they generate allot of tiredness.
I usually have her call me master too but that's more for my own satisfaction as it's only necessary if your training her as a pony girl.

Just make sure not to do it before ob is at 100.
Yes I know I skipped some stats, but most of the reason for that those stats, such as int, are already increased through one or more of the actions I mentioned and will likely be maxed just going through the steps. If not though it's easy enough just to do whatever it is a few more times.
A couple of warnings:
Pick your order carefully. There are allot of girls who I would heavily suggest having a high enough slave maker level before attempting their special endings.
Urd's housework stuff increases REALLY slow. I wouldn't bother trying to max out cleaning until your sure your going to have time. Just get it to about 2/3 of whatever your slave maker level max is then work on other things.
Save each night before Naru's night training. Her cosplay fetish get's troublesome. I don't know if it's a glitch or intentional, but a couple of her random costumes PERMANENTLY decrease several of her stats including obedience.
Ok now for the question. Hmm...I'm having issues getting Reisz's tentacle queen ending. I'm too the point were she's recruiting girls, and I got the lesbian pretty easily but I'm having issues with snow. According to the wiki
http://www.otakubell.com/smw/index.php/V3:Endings#Riesz if you attend science class often enough she'll invite you to join a club, then you have to go to the sleazy bar. That never happened in my game though, and I had her do science classes up until the game ended. She would talk to snow every once in a while but just say something about her being aloof. Any ideas?