I went to Bolivia in June / July. The weather was good. I spent most of the time in the Andes and there was no rain. Down at the Amazon area it was hot and dry.
Try not to go in August because thi is high season. It gets more crowded and more expensive.
Most of the tourists (going the first time to Bolivia) will spend most of the time in the Andes.
November to March is rainy season up there. Obviously there will be fewer tourists but roads might be blocked because of weather etc.
Keep in mind that there are various vegetation and weather zones in Bolivia. The mountain area (the Andes) is very different from the Amazonian area (jungle).
Bolivia is the poorest and they say the least developed country in South America. This influences the health care system.
Go and see a travel doc before going. Especially in the Amazonian area there are tropical diseases.
La Paz is more than 3.000m (10.000 ft) up high. So make sure you get used to the altitude before starting activities. Otherwise mountain sickness is likely. Consider 2-3 days for acclimatization.
I had no bad experience in Bolivia. Although people are poor, they were extremely friendly.
For sure in the bigger cities like La Paz, Sucre, Santa Cruz there are pickpockets but I felt safer than in Ecuador and Peru.
The infrastructure in general is not good in Bolivia. But there is what you need for tourists, so you can get along.
Either you do organized tours (like going from La Paz to Salar de Uyuni) or you take a public bus.
I made quite some experience with bus rides in Bolivia going down the mountains. You shouldn’t be easy to scare. You will be fine 99,99% of the cases but there is a reason why they called the old road the “death road”. Luckily for us, they build a new one but don’t expect European or American standards.
Bolivia was one of the cheapest places I have ever traveled. Food and accommodation is very cheap.
As always organized tours are more expensive but you get some “luxury” like transportation etc.
I always try to recommend spontaneously. If you book something in advance from home, it will, for sure, be more expensive.
I remember that I had trouble finding a tour going to Salar de Uyuni but this was because of weather and at the end I went there. So do it spontaneously.
The salt desert, Salar de Uyuni, is a must- see. It is great. Probably there is no other place on earth like this.
From La Paz you can do a tour to mountains which are higher than 5.000m (16.000ft). This is higher than every mountain in Europe!! You bus there and you need to walk only the last 200m. And that’s enough due to the thin air.
You can go to the Madidi National Park in the Amazonian area. I booked it in La Paz. You do boat tours there along the rivers, swim with crocodiles (really!), fish piranhas (really!) and look for river dolphins.
I also did a bike tour down from La Paz along the “Death road”. That was fun.
And of course, there is the Titicaca Lake close to La Paz.
Potosi is another highlight. It is the mountain of silver. Hundreds of years of mining. Big wealth in Europe came from this mountain in colonial times.
And there is more like the cities of Sucre and Santa Cruz.
As you can see from the things to do, I would suggest going to La Paz first.
From La Paz you can tour the sights mentioned above:
First acclimatization, then: Titicaca lake, Salar de Uyuni, mountains like the Chacaltaya, Death Road and definitely you should go to Potosi.
If you have been to Potosi, you understand the history of Bolivia much better!