I just like the idea that I only have to maintain the inside and not the outside.

You can purchase homes that may be a bit dated but well-maintained and in no time can get someone in to rent the property.  

In terms of a long time tenant being below market rent I would simply send them a letter 60 days prior to the end of their current lease (if that's the law in your area) and inform them that in order to properly maintain the property their rents must be increased to market rent of "whatever that is." 

I'd have it in the lease than any remaining fuel in the tank becomes the property of the owner, and that tenant must maintain a minimum fill percentage (to avoid them trying to milk it dry and you get stuck with a freeze up right after they move). 

If you find that it is excessively dirty or scratched and not maintained then send a notice.  

Put a grate of some sort on that intake so that doesn't happen again, pay for the repair, then let the tenant know that if there is every a blockage of that intake it will be their responsibility to pay because that is a result of them not maintaining the grounds.

Apparently, I maintain my properties at a higher quality than other landlords, but for something like a furnace that will be there 20 years, why would anyone want to go cheap?

Relevant individualized evidence might include: the facts or circumstances surrounding the criminal conduct; the age of the individual at the time of the conduct; evidence that the individual has maintained a good tenant history before and/or after the conviction or conduct; and evidence of rehabilitation efforts.

I inherited tenants who are on month to month lease when are purchased multiple SFR in central valley CA about 6 months back and after purchase I pass on Sewer and water bill to them (old landlord was paying for that too )I have two question :They currently pay $650 as rent and going rent in area is $850 and rental demand is high and I checked there is no rent control in city, what is good way to increase rent and how much (I am planning to increase rent by $75 to 100 and indirectly I already increased by $50 in sewer and water bill as I mentioned above).These is a lease clause where I need to maintain swamp cooler installed on roof , I want to remove that clause too, what best way to approach this, so I am in compliance.Additional note : these tenants are on month to month lease but living for over 3 years and ent in that area is increasing consistently.

But ignorer for you to maintain the property well, you need to raise the rent to the correct market value.Raise it at lease renewal.