My Democratic County party has workshops to help people who want to run for county offices. We help with forms and filing with the Board of Elections. We make recommendations for outreach to local organizations, advertising, and we help with "stump" speeches. We can only "advise" during the primary phase if there are two or more Democrats running. After the primary we do everything we can to help the candidate get elected.
For a state office the District Democratic Party helps if they're well organized. Your friend's senate seat probably covers more than one county. And, of course, the state will also help with advice. Our state has a great "advertising department" that will help with campaign material design.
Your friend will need to have a campaign "treasurer" as soon as possible. This is the most important position to make sure that they are in compliance with campaign finance laws. (Republicans like to cheat but they also like to go over Democrat's paperwork with a fine tooth comb to try and disqualify us!)
Retired politicians are always happy to talk about their glory days! Call them up, ask them for coffee to pick their brains! But remember---EVERYTHING in politics has changed! Statesmanship is gone. Being in deep red country, you know that intellectualism is disdained. There is a great book, "Hit 'Em Where It Hurts," by Rachel Bitecofer that is a must read for any politician or consultant in this era. She has great ideas about how to turn Republican tactics against them.
I recommend that you start with the legal aspects. Make sure all the requirements are met.
Then come up with the message---keep it short. Make it local. Don't run against Trump, run FOR something that is important to the people of your area. Be realistic on the message. Your friend cannot make things more affordable, and they can't pass gun control. That being said, they will be asked their opinion on all of those issues, so they should be prepared with their positions on everything!
Get a web page and facebook page for the campaign as soon as possible. Don't put the year in your print advertising (when your friend wins they will want to reuse the materials in 2 years!) I recommend that you use a local printer instead of vista print.... it shows that you support the community. Very inexpensive and very effective advertising is facebook and google ads that are targeted to the voters in your area.
Good luck on the upcoming adventure! (PS always loved your user name)
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