PhD student here + also doing full-time job. Time is your enemy.
I know a few others doing p/t Phd and those that are furthest ahead have fewer work commitments and have avoided going for promotion, new jobs etc. I've done condensed hours as I find having longer blocks of time for reading / writing to be more useful than trying to dip in at the end of the working day when I'm tired. Knowing when you study effectively is good - I can get zilch done in the afternoon and I'm better late at night. I found I was slower at learning stuff now I'm older so be kind to yourself too.
Schedule time most days for study and make it part of your routine. Have a planner of all deadlines. Plan your life around study (eg don't book a family holiday a week before a major deadline) and get family onside eg no interruptions during study time, partner if you have one takes on a bigger share of the work. You will probably need to be quite selfish so if people understand what and why, it really helps.
Familiarise yourself with task requirements and marking criteria to understand what they are looking for and look into some of the study skills for MBA books - that will save you time working out how to approach assignments etc. I've got some really good tips from these books.
I'd also throw some money at tech - I've found a fast laptop with an extension screen / extra monitor has enhanced my efficiency. Before you start your course, swot up on things like referencing software like Endnote and any specialist software you'll use. Find out what referencing system (APA, Harvard etc and what version) you will use and learn how to reference stuff properly. Youtube is good for this.
Study / writing - have a clear idea of what you are trying to achieve with a task so you can focus your reading and writing / projects.
I'd also strongly advise that you block Mumsnet on your devices as I manage to procrastinate on here so much that I could have finished months ago otherwise!
Good luck!