Pretty much all of South Sacramento between Elk Grove and Land Park/Curtis Park should be avoided, with the exception of Greenhaven, South Land Park, and Pocket (nice neighborhoods).
Tahoe Park and Elmhurst are good, Oak Park and everything south is bad.
Generally avoid anything North of the American River, and West of Business 80. That includes South Natomas, North Sacramento, Del Paso Heights and everything in-between.
North Natomas is generally nice though (North of I-80).
North Highlands and most of Foothill Farms should be avoided. Especially North Highlands. The closer to McClellan Air Force Base the worse it gets.
Some parts of Arden-Arcade should also be avoided.
Particularly the Northern part. Areas like Howe Park, Wyda way, Cottage way, Marconi Ave etc can be dangerous. Basically any place that has a collection of low-income rentals.
Parts of Citrus Heights, Carmichael, and Fair Oaks can be sketchy, but for the most part those are pretty nice areas.
The most popular neighborhoods in the city are Midtown, Downtown, East Sac, Land Park, and Curtis Park.
Tahoe Park, Elmhurst, and Med Center (North Oak Park) are also popular. West Sacramento also has some great things going on on the other side of the river. Greenhaven, South Land Park, and Pocket are the more suburban nice parts of the city, located further south.
If you don't want to be in the central city, generally the further out you go the better.
Folsom, El Dorado Hills, and pretty much all of South Placer County (Rocklin, Roseville, Lincoln, Granite Bay) are all idyllic suburban paradise's.
Further in than that you have nice suburban areas in Arden (some of the richest neighborhoods in Sac are in Arden near the river), the areas around Sac State, Fair Oaks, Carmichael, Orangevale, La Riviera (except for a couple of areas around Folsom Blvd and Watt Ave), most of Citrus Heights are all nice.
Elk Grove is a big middle-class suburb.
Generally a pretty nice, safe place. There aren't any ghettos in Elk Grove, but it is very close to South Sacramento, especially in the northern part of the city, so there is some spillover in crime. Most of Elk Grove is very nice and there are plenty of upscale suburban areas.
Generally anything south of Calvine Rd is fine.
Rancho Cordova is a pretty diverse middle-class suburb. There are some shitty, dangerous neighborhoods, and some brand-new nice neighborhoods, and everything in between.
Just don't buy or sign a lease without checking out the neighborhood and doing research.
Sacramento is weird in that we have some really dangerous neighborhoods that are right next to some really nice neighborhoods. Often only separated by a freeway, railroad tracks, or major road. For example Meadowview is a very dangerous neighborhood separated only by an overpass from Pocket, a relatively wealthy neighborhood.
Also, depending on where you're from, a lot of our "ghettos" don't look like ghettos.
They look like typical suburban neighborhoods with single-story homes and relatively decent looking apartment buildings. Looks can be deceiving.
Do some research and ask questions. Check police records. Don't be silly.
Looking back on this, I forgot to add Hollywood Park into the nicer neighborhoods of the city. The area around Fruitridge and Freeport is a nice, quiet middle-class neighborhood that doesn't get enough love.