How much do you emphasis do you put on design thinking, as a marketer, when you design a marketing campaign?

I believe perfection is very important is presentation and i would try to put100% effort on Design 

In my opinion, design thinking can help marketers design better storyboards in shorter spans of time because the branding, focus group testing, team-building exercises and copywriting gets tested in the before launch.

Design gives an layout of how your campaign would look & based on the Target audience it would be laid.

An successful campaign is not only 'What you portray or offer but is also 'How' you are going to promote your product'.

In an FMCG perspective: Much before an actual campaign (Major) starts the design in terms of 'Give away's', 'Freebie's', type of promoters, how they present, what message to give, hooker's, type of outlet/chain, Lucky draw (Optional), type of In-Category promotion which would be in align with the theme of the campaign everything should planned.

Thus, the blueprint which we get is nothing but 'Design of Campaign' & this gives perfect edge to make changes & an base to make it more successful. :-). 

When: It will vary brand to brand - For Example: Food brands usually prefer Pre & or Post Ramadan period (June to Aug) or Nov & Dec (Between Christmas & New Year), it's just an suggestion as campaign is mostly driven by Objective of doing it. 'Back to Home' or 'Back to School' period between Jan-Feb or Aug - Sept: As it is also a good period for brands which has more focus (Or it's Target Market) is Kids or children. :-)

Definitely too much emphasis on design thinking while making any marketing plan because, it is the methodology that imbues the full spectrum of innovation activities. And this innovation is powered by a thorough understanding, through direct observation, of what people want and need in their lives and what they like or dislike about the way particular products are made, packaged, marketed, sold, and supported.