My main advice is: Be wary of choosing large and/or cheap registrars.
Big registrars can’t afford any support costs since they prefer to squeeze the price down as far as possible, and therefore they prefer to simply lose or outright drop any customer in case of any and all problems. Conversely, small registrars may charge more, but have better (i.e. actually existing, and sometimes even dedicated and personal) support for when things go wrong, and have a vested interest in keeping you as a customer.
A small registrar might also be so small as to know you personally, which will help monumentally against any social engineering attacks.
(I work at a rather small registrar, with lots of small clients, including lots of private individuals, but also some very big customers; i.e. company names you might recognize. We aren’t cheap, but our support is worth it to our customers.)