It's difficult this, because it's very personal. I'd suggest that there are two ways you can approach this, and it's probably best to mix the two.
Firstly, what areas of experience of knowledge would you like to gain over the next one year and next three years? (Those periods aren't "set in stone", I just find they work quite well.) These could be things you are interested in, or things you feel you should do to develop your career. Getting experience of a new software language? Spending more time with customers to understand their needs? Learning about your company's legal compliance process? Then capture how you might be able to do this. What do you want to do. Why do you want to do it. How do you plan to do it. When to do you plan to do it by.
What: Gain experience of the next generation PLC system and programming.
Why: To be able to provide support to the update of the control system to the new PLC platform
How: Attend suppliers training course. Secondment to the team carrying out the trial introduction of the new system.
When: By October 2019
It's pretty clear that "How" and "When" will need to be agreed with your line manager - but if you go to them with a good "What" and "Why" there's a good chance they'll agree it! And of course some of these will actually come from your line manager.
Secondly, after you've found the development actions that just come up in the day job, have a look through the competences of UKSpec for the level of registration that applies to you. This may well suggest further areas where you are competent, but could still gain more expertise. Or where you have to be careful that you don't get left behind. So taking a typical one of "E3 Undertake engineering activities in a way that contributes to sustainable development.":
What: Improve understanding of company's processes relating to safe disposal of equipment after removal.
Why: To ensure my work is fully compliant, and to look at ways that I may be able to reduce the environmental impact of my projects.
How: Attend briefing on WEEE directive. Arrange one-to-one session with site lead of HSE. Support environmental audit of next refurbishment project
When: By December 2019
How you lay it out is entirely up to you, and it may well be that you are already using an annual appraisal system in your company that captures this sort of thing - in which case I'd suggest use that! You don't need to invent something new. But if you do have to create something new don't get too worried about the format - my main advice is just that however you lay it out you use the "What/Why/How/When" structure.
Hope that helps,
Andy Millar CEng CMgr IET Mentor / IET PRA
A slightly different perspective on top of the existing good advice:
If you already have work based appraisals and planning, then select one or two of the work based development tasks for your personal plan based on what is good for you. Often work based 'development' tasks are really corporate programme management activities rather than personal developmental. Seek out the personal developmental aspects within. A DAP is about YOU, not them.
Identify a (few max 3) long term development aspects as personal goals. These should have shorter and longer term improvement points within them. Be flexible. It's a the tortoise that won, not the hare.
Make sure that you write up you development, especially if you are going for registration. You will need the practice in writing personal concise statements of you competence examples. Most corporate writing is, relatively speaking, waffle - you weren't there, you didn't do it, someone else gets the credit.
Do ensure you reflect on your development, and be able to say "that was me. I did that. They <key facts> (that can be checked) were.." The latter skill is very useful for corporate annual appraisals because they become statements of truth that cannot be denied (and it helps you managers remember what they needed to say about how good you were..)
As per competence D, create your own 'form' (or adapt someone else's). Structure it so it says what you want/need it to say.