It is really important for you to appreciate that what employers want more than anything is sufficient relevant prior experience ("SRPE"). They want it because:
(a) training courses (with a few honourable exceptions) tend not to be as good as good SRPE; and
(b) they don't have to pay so much to train you.
Minimum experience wanted
The minimum period of SRPE is six months. Less than that won't hurt your application, but won't get you into the "experienced" category. Many employers look for a minimum of a year's SRPE.
It follows that any work placements you did don't count for much. For sure mention them in your application, but don't bother to overstress them as it will just undermine your credibility.
What constitutes "relevant" is fuzzier. If you have nine months experience doing family law work then it will be very relevant if you apply for another family law position, but much less so if you apply for a conveyancing job.
Relevance applies to skills learned as well as technical legal knowledge. Maybe in a previous non-legal job you learned negotiating or interviewing skills, IT skills or how to handle clients in a professional environment? Wherever possible talk in terms of transferrable skills.
To see which skills are valued, look at the Introductory Level National Competency Standards.
Any relevant prior experience is helpful. Where you got it matters little, for example many successful paralegals first worked as part-time Citizens Advice volunteer advisers.