You can split doctors into GPs, Treatment and Research.

GPs - GPs focus purely on diagnostics, and obviously the GP diagnosis skill if possible. You want to avoid allowing GPs from working in treatment facilities such as the Pandemic room as without sufficient training they are likely to kill patients leading to a drop in reputation as well as loss of income and morale. Generally speaking, training your GPs is a low priority, as well as their room prestige level, although if you find them overloaded with patients then it can be a good idea to train them instead of hiring more doctors, which is much more expensive.

Treatment - You want your treatment doctors to have as high as possible skill in treatment as possible, to minimise deaths. As well as the treatment skill itself, there are various other ways to improve this which isn't so obvious. You want to give your treatment doctors high levels of prestige rooms to give them happiness buffs such as 'amazing room' and 'attractive environment'. Why? Because once they reach 80%+ happiness they gain a further 10% to the treatment skill. Further more you can increase this by another 10% by giving them sufficient break time and keeping them 'energized', also helped by supplying them with energy drinks/coffee. Another important skill is Emotional Intelligence, which can further help you reach that 80% happiness threshold with an additional 10% happiness. Also keep your eye out of other important traits such as 'positive' for another 10% happiness, and it's important to note that each star rank boosts them by a further 10% treatment skill. Above all make it a priority to train your doctors in specialist skills such as psychiatry for a 20% treatment boost. Be sure to uncheck your untrained doctors from working in the treatment rooms and leave the job for the pros. ;)

Research - It's important to understand that researchers do not receive a research buff from happiness. It is therefore unecessary to provide them with high prestige facilities. You want to instead fill their rooms with as much research buffing equipment as possible, or you are otherwise fine with keeping their facilities to an absolute minimum. It is best to focus all their skils slots into research, right up to level 5. It's entirely possible to run a hospital solely on research as you gain a £10k grant per research project completed. This is achieved by gunning for the general research project, and you can easily make a tidy profit if you make use of 5 researchers in one room, even if theyr'e at level 1.

You can split Nurses into diagnosis and treatment

Diagnosis - Much the same as GP's, set any of these nurses to work in any of the facilites focused on diagnosis, such as general diagnosis and the cardiology. As long as they are not working on any treatments than their training is at a low priority.

Treatment - In certain rooms such as the pharmacy and clown clinic which focus on curing patients, you want to ensure your nurses are maxed out in their treatment skill, just the same as with the treatment doctors. Just make sure that you seperately train your specialist staff with the respective skills, such as in the ward, for maximum efficiency.

Assistants are relatively simple to manage as their training is a very low priority, simple put, assistants aren't very important, I apologise for any of you real life receptionists out there... XD
One thing you wnat your assistants to be is efficient, as the worst that could happen is to have a long qeue... Well I've tested this and basically how it works is that for each rank and each levels of skill in customer service, your assistants will serve customers faster. Their happiness buff also increases customer service by 20%, as well as another 20% from being energises. So if you want to make sure you can handle the qeues with as few receptionists as possible, then give them high quality surroundings and keep them well rested. Also for this reason it also makes sense to give them the emotional intelligence skill.

From my experience hospital reputation isn't particularly difficult to increase, so as of yet I feel like it's not effective to focus on the bedside manner trait with any staff, but I will test this further as I could be wrong. Energy training however could be a good choice to ensure you're hiring as few receptionists as possible.

There is another buff that assistants receive from happiness which is +%20 in marketing. Like teaching, marketing is another situational job which can be useful and it makes sense to have separate assistants trained in it. From what I can see, it makes sense to encourage patients of a particular illness then focus your nurse and doctor training to cure that illness, and level up your facilities in that area. I haven't yet experimented with using marketing to boost reputation as I haven't found a need for it, so I'm not sure yet if it's worth it. I don't know if it's just me but reputation just doesn't seem to do much good, I'd like to know if it at least affects the prices people will pay, in which case it would be amazing, but I'm still yet to test this out.

The 2 most important skills for a janitor are the maintenance and speed skills. No other members of staff have to rely so heavily on speed, as janitors need to be in several places at once at all times. Fortunately there are many ways to buff a janitors speed skills, once of which is being energised. Supply them with a coffee maker in the staff room, or an energy drinks machine and watch them dash around the hospital like a junked up lunatic. Also look out for the 'motivated' skill for an extra 20% speed. Happiness doesn't boost their speed, however being unhappy reduces it so be sure to keep them satisfied so as they don't mope about. It can however be a benefit to keep them happy is it gives them a buff to maintenance, particularly for a janitor who's specialised at maintenance tasks.

Janitors as well as researchers are the only staff types which don't suffer from negative social traits as they don't interact with patients, so feel free to hire them without repercussions.

As you might have noticed, hiring guest trainers can be a very expensive ordeal. This is why it is important to establish a 5th class of staff type which isn't made so obvious in the game. You can house your own roster of highly trained teachers to train up swathes of junior doctors for absolutely no cost, save for their wages. For this strategy it then becomes important to make your teachers as efficient as possible in order to see returns, such as buffing the teaching skill. Look out for the training masterclass skill, and train up your teachers themselves in this skill for a massive 50% boost. Also look out for the Teacher train which gives another 50% teaching speed buff. There are also several items which boost a room's teaching speed such as certain posters and the anatomy/skeleton display, so add these to your class rooms. There's a $5k payout for every class completed, although it's unclear whether you receive this payout for all of the students in each class, so play around with it.

Not everything is so cut and dry with this game as the systems and mechanics are quite in depth and allow for quite a bit of experimentation.

-For example you can create treatment or diagnosis doctors and nurses which instead of being specialised are used as on hand staff which can react to different illnesses. With this strategy you want to focus on the speed skill to ensure they can get around the hospital efficently.

-There are also multiple other very useful traits such as 'cheap' and 'tireless' which can save your money in the long run, so look out for these if you're on a budget. The romantic trait can occasionally give your staff a happiness boost when they fall 'in love', and a member of staff also receives a happiness buff if they receive a reward, or cure a patient, to name a few.

-Also if you're using a lot of plants to increase the prestige of your rooms, think about allocating them to staff with the green fingers trait so they can alleviate the massive work load from the janitors by watering their own plants.

-And lastly, consider placing food and drinks objects for your staff in their rooms so that they can recuperate their hunger/thirst between patients. Although this only works if it's not too busy. Also it's beneficial to keep food and drinks objects within the staff room. Staff when on their break in the staff room receive a constant happiness and energy gain while inside, so you want to keep them in their for as much time as possible, and not have them spending their break running around the hospital.

-It is entirely possible to work staff without a staff room by refilling their energy with coffee or energy drinks. This works particularly well with researchers or any staff where happiness is not important. There are however also several items which increase happiness, I've not yet tried this, although this shouldn't be necessary as staff receive a constant happiness gain by working in a high prestige room.

Thanks for reading my guide, I hope it was very informative and helps you to get more of this wonderful game. If there's anything important I've missed feel free to drop a comment. I'd love to hear your tips and tricks.