In contrary to almost all sub saharan African countries, Botsuana saw steady and strong development right off the start. While most neighboring countries decended into civil unrest or civil war or saw strong men taking over power, Botsuana build up a relatively stable, democratic and free political system. While most African countries suffered economically, Botsuana saw steady development. When it comes to human rights and corruption Botsuana seemed to have performed the best from the start. What are the reasons for the difference, especially when compared to other ressource rich African country that seem to have fallen prey to the ressource curse?
Short answer: Discovery of diamonds just after independence (around 1967) provided a solid economic foundation for their development in the post-colonial era. This combined with the 1895 declaration of Bechaunaland as an Imperial Protectorate, rather than a chartered colony under the rule of the British South Africa Company (BSAC), meant that they had always been relatively independent and did not suffer to from direct colonial rule to the same extent that Rhodesia/Zimbabwe, Zambia, Namibia did. Essentially they started their post-colonial development already several 'steps' ahead than other neighbouring former colonies.
Slightly longer answer:
Relatively small and largely political unified population reduced the chances of civil strife or inter-ethnic/political violence. In countries like Angola or Zimbabwe where a large population comes from ethnically diverse backgrounds, sub-national conflicts are more likely to occur, especially around the times of independence as the power and money of the new nation come up for grabs. This did not happen in Botswana, meaning resources were not diverted or fought over within these conflicts. Furthermore, a small population means that a greater amount of money can be spent per person, thereby reducing the huge inequalities that spring up elsewhere. Which leads to my second point....
Lack of settler population: Unlike Southern Rhodesia, Kenya, and South Africa, there was never the settler influx that dictates political and economic development. In colonial Zimbabwe, for instance, the imposition of a direct settler rule impacted the economic development by restricting African agriculture in favour of white commercial farming. In the short term this provides large profits to the settlers but ultimately means a big chunk of a nation's renewable resources (i.e. cash crops instead of mining/natural resources) are exported and the profits are similarly external. As mentioned in the short answer, Botswana was not under company rule (although they were under the High Commission). This meant profits stayed (mostly) within the nation and were (mostly) reinvested into infrastructure and development. There also wasn't a small white minority population (like in Zimbabwe) controlling 85% of the nations wealth and most arable lands post-independence.
Natural resources: Diamonds provided the initial economic boost during the early post-independence years and provided the stability that permitted wildlife tourism to prosper. Places like the Okavango Delta were quickly marketed as excellent and unique safari destinations. The security provided by a stable nation was particularly appealing during the 1980s when South Africa, Zimbabwe, Angola, and Mozambique were all experiencing domestic conflict. This is a renewable resource and therefore provides a steady income to local communities as well as leading to a good....
....reputation within the wider world: In the late-1950s through the 1960s and up to the early 1980s, Africa as a whole experienced widespread and often violent decolonisation episodes. Although Botswana provided support to many liberation movements as one of the Frontline States, they never actually fought in any of these liberation wars. This gained them a reputation within the UN and western powers more generally as a nation that was a secure investment, and more importantly, had a strong, stable, capitalist and pro-western government. Unlike Julius Nyerere in Tanzania, the ANC in South Africa, or the Zimbabwean nationalist parties, there was little to no interaction with the communist USSR and China. This meant the USA in particular was a very willing purchaser of Botswana's resources and to support tourism efforts. Should also mention that the discovery of diamonds in 1967 led to the huge De Beers company having a vested interest in the continuing stability of Botswana so they could continue to work the mines - this corporate buttressing was taken as a good sign by foreign governments who were willing to follow their lead. It also endeared Botswana (bizarrely) to the apartheid government in South Africa, despite the former's hosting of MZ (ANC's armed wing) guerrillas within the nation.
I don't know if I can go more into anything (perhaps the pre-colonial era?) but two great books are Neil Parsons' King Khama, Emperor Joe, and the Great White Queen and Sampson Jerry's History of Botswana