This is in some way for children, but it may help you:

http://www.cursosinea.conevyt.org.mx/para_asesor/auto_asesores/cd/lengua_comunicacion/vamos_escribir_2e/02_ve_manual_2a.pdf

...and one more, this one I stumbled upon yesterday but really liked the suggested sites (especially Euronews, awesome resource to listen to news clips and see the transcript as well. I might just start getting my daily news from there):

https://forum.wordreference.com/threads/general-resources-recursos-generales-please-contribute.2220250/

Hi Andy,

Surprisingly the first result in Google search was actually the one I've used in the past, and found to be useful as a primer:

https://studyspanish.com/grammar

It should work perfectly to get you familiar with the concepts in a well-thought order. If you find any of the concepts needing more thorough explanation, you may need to just look for another site or even Youtube videos that offer additional details and examples.

Hi Andy,

You can try with this link: https://marcoele.com/gramatica/

In this place you are going to find language teaching and learning resources.

Regards.