The 'Do It > Twist It > Solve It' or 'Do It > Secure It > Deepen It' lesson design structure created by Steve Lomax (@MaxTheMaths) supports a teaching for 'mastery'  teaching for 'secure and deep understanding'  approach. It has been used in hundreds of schools since 2014 and the lesson design was inspired by a mathematics visit to Shanghai and working with schools in the UK, in particular the outstanding Headteachers Karen Horne (Mansfied Green Academy) and Anthony Mitchell (Glenfall Primary School). It embraces the core principles of Variation Theory by supporting teachers to design examples and exercises to secure and deepen pupils' understanding of mathematical ideas by highlighting essential features of a concept through the use of:
 'What it is' (standard)
 'What it is also' (nonstandard)
 'What it is not' (nonexamples)
 'Apply understanding to solve familiar and unfamiliar problems'
The use of labels 'Do It, Twist It, Solve it' / 'Do It, Secure It, Deepen it' ... Do It, Bop It, Zap it, Kick It, Whack It (now that's just being silly) is pointless without respecting the pedagogcial principles behind them. Some schools have decided to change the labels  which is fine as long as the principles are valued and not changed  otherwise the lesson design will not have the desired impact on pupils' learning and outcomes.
Can you ‘DO IT’? 
Focus on the ‘What it is’ and 'What it is also' Simple, standard examples followed by nonstandard examples to challenge procedural fluency. 
Are you SECURE? 'Twist it'

Focus on the ‘What it is not’ Active argument tasks  eg True/False, Do you agree?  focusing on misconceptions and opportunities to reason about teacher initiated mistakes to challenge conceptual understanding 
Can you apply it to DEEPEN your understanding? 'Solve it' 
Opportunities to apply understanding by solving familiar and unfamiliar problems including empty box/find the missing symbol, ‘Here’s the answer  what is the question?, Always/Sometimes/Never, etc to challenge mathematical thinking 
It is also important to note before pupils tackle activities, they have the opportunity to explore the mathematical idea together during a 'Teach It' (Use of a 'Hook' to introduce the concept, Modelling, use of concrete and pictorial representations, etc) phase and then have an opportunity to have a go at trying some examples together in a 'Practise It' phase.
Pupils then have a go at 'Do it > Twist it / Secure it >Solve it/ Deepen it' tasks to challenge procedural fluency, conceptual understanding and mathematical thinking.
A coherent scheme of work with clearly identifiable ‘Conceptual Themes/Big Ideas’ broken down into small 'Key Learning Points' is essential to support the lesson design. www.mathsnav.com is an ideal medium term plan to use.
The design also ensures the aims of the National Curriculum are a feature of every maths lesson and supports 'differentiation by depth' rather than moving too quickly onto new content. The acronym DEPTH is a useful reminder about the key startegies:
D o you agree? 
E xplicit use of misconceptions and mistakes 
P robing Questions 
T he missing digits/symbols 
H ere is the answer what is the question? 
Note: The lesson design is a framework to help plan and teach for secure and deep understanding. It should be used flexibly and there will be lessons when it is not suitable  eg lessons designed for pupils to explore/investigate/discover a new concept or solve more complex problems that bring together several key learning points.