i had an earlier post that should give any new player the basic first steps to not fail on any slave since it was a reply about temperament. The wiki has all the info you need as well, it has a guide for playing one of the harder chars which translates over to any other char you may choose to play. but ill put some basic tips here
use 3 rules at all times i recommend cook, maid, deny orgasm, and deny masturbation as your first 3 (can use all 4 if you want).
I'm four more beers in than I was last time so my apologies in advance. The 3 rules thing is entirely valid, on my current playthrough as Johnny (Nerd in this version) I've found great success using "force humility" (builds obedience quicker, the only negative effect is lowering pride, which I'll talk about later on in this post.), "bath slave" (only negative is it decreases her arousal) and finally, "force rules".. Which counts as a rule. Don't question it. Other really good rules are "vaginal vibes" (builds arousal which you can use to reward her sexually, or use the active sex option for.. sex. Also raises empathy.) Behave: Alarm is also decent but not necessary.
make sure beauty is high enough to reach the required rank in your slave
don't over punish but don't under punish
By this he means the number next to the reward or guild thing under the slave portrait. If she has a "2" you want to use the second option. You can hover over the little arrows on the punishment icons to see what number it is, generally, it's in the list order. One exception to this is the "award free time". That list is out of order.
don't spoil your slave if you do use the put in place chat option
Spoilage occurs by not punishing her, by rewarding her too much (more than twice on Classical/Hardcore which is what I play and I don't remember the lower difficulties). Spoilage also occurs if you allow her fresh food before she is devoted if you allow her to sleep in your bed before she is devoted, and a few other things cause spoilage.
use the encourage to help with mood
If you do this too often it'll stop helping. I usually use it every few days, the important thing is to keep track of your slaves' stats. (You can click on the stats in the left-hand menu when you click on the book to train her to see the numbers).
haughty and arrogant slaves spoil faster and are harder to build obedience get a leather collar and train enema, in the beginning, to help lower pride and build obedience.
naked walk and shameful podium lower pride as well when they misbehave.
I'm going to add in a huge caveat here. If you lower pride too quickly, your slave might break. Which means she's useless except for, pretty much, one quest in the game. I recommend you stay away from prideful slaves in the beginning. They take longer to train, they can break if you're not careful, it's just not worth it.
keep your slaves happy give them a sun dress asap, the first positive 5 achievement promise a gift then second time make gift sun dress this has a huge impact on their mood.
My own strategy is to give them the dress once they are obedient and I don't need the anal tail anymore. Also remember that you want to give it to them as a reward since you can also buy it at the boutique.
fresh food is similar to a small reward take it away if you cant get spoilage to drop but it greatly helps with mood so use as much as you can.
I disagree since I find it easier to build obedience and have a slave feel alright than it is getting rid of too much spoilage.
don't be afraid to invest in the barn once you have some sparks saved or if you accidentally broke a slaves mind it will nearly pay your rent if you have a cow chicken and farmhand and are overfeeding them (mature are best for cow and chicken but any slave will work till you have more sparks then you know what to do with.)
Another caveat is that you need (I think) to have a manager of the barn. The manager needs to be devoted enough to be your assistant (which you'll know she is if you get a button with an upwards green arrow and downwards red arrow in the right-hand sidebar).
always take a new slave to the technospheere and have them checked out (even from the guild) often they are pregnant and that's bad since the slave can be taken away and if pregnant by a fog fiend they will die.
If you have enough doctor skills you can buy a stethoscope at the Guild Hall and you'll get a red icon in the bottom left-hand corner of her portrait when your slaver thinks something is amiss.
certain skills raise endurance as well a temperament like dancing, the higher your endurance the more action points. 3 should be enough for a d rank slave 4 should suffice for c and anything after that i recommend maxing endurance.
I usually only go for B if the slave is staying for a while. If I'm only going to make money by selling her to the real estate agency (for which you need B+ Etiquette, B+ Clerical work overall rank D+, which means two more skills need to be B+) I won't bother getting a slave below A+ endurance. With A+ endurance I can easily sell that slave on the maximum difficulty in about 10-19 days. She buys them for 750 and I don't think there's an actual limit to how many she'll accept. So there's a tip from me on how to make quick and easy money early game. Sell them to the real estate agency.
think i covered what you should need to not fail on pretty much any slave (i have trained slaves that most would just mince or not take on). if i did not cover something ask ill add it to here and sorry its not better organized.
Thanks for making this post! As you can see I've added a bit of my own advice and stuff and things to it.
I'd like to add that in the beginning, you might want to just buy slaves that cost 20 sparks. Profit margins and all that. The absolute best money is selling slaves at the guildhall during the auctions. I believe B+ slaves are the best bang for your buck. Speaking in terms of time to train versus return on investment. But in the early game, go to the residences and see what they want (spoiler: most, except for the outcasts, want assistants as D+ slaves). You'll get 500+ with lower profit margins than the real estate agency because you'll need to spend money on getting their style and exoticism up. You do that by getting them piercings, tattoos, clothes.. Stuff like that. The reason you want to sell to the residences is that you get increased reputation with their faction, which, after a single sold slave, allows you to buy a house in their quarter. After enough you've gained enough rep you can then become a patrician of their house. However, choosing a house will exclude the others. Or something. I've only ever become a patrician in White Town (Cuz it's Effing White Town, Ballestreet and all that). Also, everything that's not quoted in this post is my own opinion and disclaimers etc. I think.
I feel like I'm rambling about something and I should probably stop. Also if Grammarly doesn't clean this post up so it's readable, God help you and I'm sorry. Here, have a