Depends on how much control you want to have and how much money you want to spend.
One the one hand you can spend a few bucks on tape-on thermometers, and move the vessel around different temperatures in your house. That's what I do.
On the other hand you can spend thousands on a conical fermenting vessel of stainless steel with a water jacket that allows you to control the temperature to a degree.
In between it depends on if your environment is too warm or too cold. If it is too cold there are wrap around heaters that are less than a hundred bucks.
If it is too warm you will need some sort of refrigeration and thermostat combo. That can cost hundreds.
In my case I don't brew in the height of summer because there is no place I can put a primary without it reaching the low 70s between ambient temp and the heat produced by the yeast. Otherwise I monitor the temp and try not to let it get over 70*or much below 60**. As I type I have an ale in the basement vigorously fermenting at 62. If I wanted to warm it I would wrap it in a blanket and let the heat produced by the yeast warm it a couple degrees, but I'm experimenting with what happens when an ale is fermented in the low 60s.
You can read all the books in the world but the only way to know for sure it to try it.
My next batch will likely be a lager, and by then the basement will be in the mid to low 50s. This will allow me to keep fermentation in the neighborhood of 55**. By spring it will be back to ales, and no brewing happens in the summer.
* Ale fermented above 70 can end up tasting like banana. Not good.
** Ale yeast can go dormant at temps below 60.
*** Lager yeast can go dormant below 50 and while it will ferment at ale temps it is best if fermented under 60. Fermented at temps above 60 the finished product loses the lager crispness and becomes "steam beer".
Hope that helps.