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- Always test any customisations before and after a new Salesforce release. That's a given.
- Always build flows and processes in Sandbox then deploy them to Production (yes, I know, deployment of Process Builder and Flows is kinda hard).
- Run your test classes often, to make sure that you haven't broken anything that code relies on, or your future deployments will become a nightmare.
- Know what's in code and what's in declarative tools. In the perfect scenario you will have it all documented.
- Know what the managed packages in your org do - especially if you have tried to extend the managed package with any declarative options or code.
- As an Admin, when you click a button, know what it does. You should know this even more than your developer knows this.
The Line
So where to draw the line between Clicks and Code. Well that is up to you, and depends on your business and what sort of budget you have to implement the system that is going to transform your business. There is no definitive right way, Start with Clicks, but know that you may want to move to Code when Salesforce becomes more of a mission critical part of your business. I would say never start with Code because if you are just starting with Salesforce you will never know enough about how you and your business will use Salesforce to get the benefit out of spending that money up front.
Remember, this advice is aimed squarely at small to medium businesses or NFP that does not have a team of dedicated, experienced Salesforce developers on staff.