Advice from practice in my own city based on a comrade's efforts at organising tenants. Pick a campaign, rent hikes are a good start. Use municipal information (if possible) to assess how many and which landlords hold properties, in our campaign we used the rates (city taxes) information as declared by landlords. Once you have identified good sites to start with e.g. Buildings with a single landlord, go door knocking and talk to people about the rent hikes and seek their level of anger and willingness to act, ask them about actions they might like to take, suggest some actions - could be staggered rent payments to make an admin nightmare for the landlord, in our country this can incur an extra accounting cost for the landlord and spread over a block of flats can be pricey, or it could be rent strikes. Once you identify some leaders amongst the tenants, organise the actions with them, don't needa use the big C word at this stage of a campaign. After the campaign keep contact with those people, assess what worked and what didn't. Rinse and repeat.

I appreciate that was a bit of a ramble, happy to have a fuller conversation around any specific details that are unclear or lost in the jumble

https://www.rs21.org.uk/2015/06/12/1915-glasgow-rent-strike-how-workers-fought-and-won-over-housing/