best way to advertise a local painting company

How would you go about advertising a new local painting business. GBP already established, zero review and zero customers yet.

What would be the best platform to advertise on and any advice?

Try to target more specific keywords (even if they are long ones), they gonna give you more precise jobs and also help you to rank for primary high volume keywords.
Join local community groups on facebook and other platforms and post about your recent works and keep engaging people.
Ads are good option for the start but I'm not the right person to give you advice on that.
Hope best for your business!!

Giving advice with very little context only makes the response more general. Try to be more specific. BTW, these are my first comments in this community, so ignore if I have made a mistake.

I'd start with Google and local Facebook groups. Get a few jobs through referrals, take photos of your work, and ask happy customers for honest reviews. Once you have some traction, test Google Local Services Ads or Nextdoor before spending much on ads.

google + fb, buying posts in local communities (local news) in social sources

Since the paint industry is highly localized—with customers typically hiring painters or purchasing paint from the nearest store—you need to optimize your PPC campaigns.

Have a Roofing company, we get decent leads from GMB but the best leads are usually from paid ads. I'd say go with Meta ads and they will be well worth it, GMB and trust stuff take time.

Also, do not hire from here. Most spam links, do whatever so you can paythem but no real impact.

If you are having a new painting business, your first problem is the zero reviews. Actually, it burns your ad money until you fix that.

So first, fix your zero reviews. you can pay in something cheap at no cost for friends and family and get some reviews, then post your before and after in social media, local groups everywhere possible and then only you must try local search ads and Google search ads.

From there, you can easily move on to the next step. We have been trying out a lot of GBP recently, particularly the new ones, and we follow the same format for gaining the traction, and it is doing really well.