I think the main focus has to be a clear monitoring process which is properly explained to staff so they know what's expected of them (or can't pretend they didn't know). From a UK perspective, the 4 main areas to focus monitoring on will be books/marking, lesson obs/learning walks, pupil voice and planning. In my opinion, the most important of these, in terms of telling the SLT what's actually going on in the classrooms and the quality of teaching over time, is the books.
So start with a staff meeting when everyone agrees together what a decent set of books should look like. How frequently should there be work in the books? What presentation standards do you have? What is your marking policy (if you don't have one, write one together)? Are you expecting pupils to respond to marking? How many pieces of work a week should be marked in depth and how many can be "tick and flick" acknowledged? All of those things. Come up with a list of expectations for your school which is circulated to everyone. The marking policy should be displayed in all teaching rooms in the school as well so if a TA/student/volunteer marks the books of a group they've been working with, it's easy for them to ensure their marking is in line with the school policy.
Give it a couple of weeks. Collect books in and do a book scrutiny - check them against the agreed list that everyone wrote together. Give individual feedback to those members of staff that aren't following policy. Listen to their reasons why they say they can't do it and give them strategies/advice about how to do it. Give it a couple more weeks. Do another book scrutiny and feedback to staff. Expect it to take several runs round this cycle to start to see an impact.
Once you've got books/marking starting to be done in the way that the school wants, then you can move on to other areas. Probably learning walks/lesson observations. Follow the same cycle. Agree together what makes an outstanding lesson and what, in an ideal world, should be happening in the classroom. Then SLT get out there and see if it is happening or not. How often are your SLT out and about round school? Do they drop in to deliver forgotten PE kits or messages about changes to who is picking a child up? Do the children see them on a regular basis? Or do they sit in their offices and rarely appear around the school?
Following this approach has several benefits. It means that the "slackers" can't use the excuse that they didn't know what was expected. If everyone is involved in the development of the standards expected, they should be more committed to achieving them. It allows SLT to praise staff who are doing well and draw attention to good behaviour. And it allows SLT to pull up those who aren't complying.
If you are in an international setting then I assume you've got a lot more leeway than UK state schools to decide what your school expectations are. In my opinion it matters less what you agree on than that those standards are enforced consistently and fairly. As a hard working teacher who always tries to do what is expected of me, I get really pissed off when I see colleagues slacking. So following an approach like this should help to motivate those who are doing a good job. I suspect you'll find there is another group who have lost their way a bit and doing this will help them to see what they should be doing. And then you'll have a small group who aren't prepared to change. Following this sort of monitoring cycle will help to gather evidence should the SLT choose to go down a disciplinary route.
But most of all, it's fair and above board. Everyone is treated in the same way - no favouritism. Everyone knows where they stand. You've created a format to praise those who are doing a good job - like working with the children, you draw attention to the behaviour you want to see more off.
And I agree with people above who've said that the biggest motivator for them is a Head who knows what they are doing and is interested. The HT I've been working for since Easter makes sure all the children see her round the school each day. She pops in and out of rooms for all sorts of different reasons each day. That means that when she does appear for a more formal reason, the children and I are used to her being there. I know that she knows what is going on in my classroom, she comes in to back me up when one of my difficult pupils is being challenging. She also comes in to celebrate good work by the children. I'm proud of what they achieve (most of the time....) and I like the thought that she knows the impact of my hard work. Knowing that she might appear is also a pretty big incentive to not slack off.
One of the best Heads I've ever worked for was very good at making people feel good about themselves. It was a real gift she had - the fact that she clearly thought me capable of achieving things made me want to go and achieve them! That was in a school with barely any resources, a crumbling building and no money for anything. But because of the personality of the Head it was a very happy school to work in where everyone pulled together. It sounds to me as if your SLT need to be building a similar ethos.