Couple of thoughts.
1. buy a wills & probate book. Make sure it's English (or Scotish of more appropriate) rather than US law. That'll give you a good grounding in what's involved and guidance on whether a solicitor would be prudent.
2. List out who you want to leave your stuff to and in what proportions. You obviously need to do this whether a solicitor writes the will or not. Bear in mind possibility of both you and spouse both being killed in same road accident - who gets the stuff then ?
3 Appoint executors - these are the people responsible for winding up your affairs and dishing the money out. Typically would be the main beneficieries / next of kin. Whilst some people appoint solicitors as executors, bear in mind the friendly family lawyer appointed could be long dead by the time it comes to pass and his firm been taken over. In any case a normal person executor can appoint a solicitor to do all the work if they deem it sensible or necessary.
4 Write the will - or get solicitor to top and tail your wishes in the form of a will.
5 get the will witnessed. Witnesses must not be left anything whatsoever in the will. Read up exaclty how to do this if not using solicitor.
6. I would do and have done a "straightforward" will myself but would , and have got a solicitor to do a more complicated one ( divorce related).
7 I'm dubious about "will writing" services. Have used one once and though job was just about OK I knew more about it than the guy in question
