1. Try not bring USD
The major legal currency for Cuba is the Cuban Convertible Peso (CUC) even though there’s also the Cuban Peso (MN). Most tourists will only ever deal with CUC.
Don’t take USD dollars since you will be subject to a 10% special additional tax or commission. It is also known as the gravamen. Euros, Canadian or Sterling are fine to take and are widely accepted in Cuban money exchanges/banks. The exchange rates are generally quite reasonable.