If you are being funded by a university, national, or international funding body for your research, it is likely the funder will have requirements about research outputs (including publications, underlying data, and conference presentations) being published Open Access.
If you are unsure of your funder's requirements, you can use the Cambridge Open Access website's guide to funder open access policies to check. The Sherpa Romeo website will help you find out whether a particular journal allows Open Access publishing or self-archiving. Cambridge Open Access also has a guide on publisher policies.
The University of Cambridge also has 'read and publish' agreements with a number of publishers. This means that authors can publish their articles open access with the journals covered by the agreements, without paying a fee -- provided the corresponding author has a University of Cambridge affiliation. You can read further details (including a list of the publishers with such agreements) on the Open Access website.
Generally it is a requirement that all University of Cambridge research outputs (PhD theses, articles, books, datasets, conference presentations, and more) be deposited in the institutional repository, Apollo.
When choosing the right journal for your publication, you may need to balance several different factors. These are likely to include:
What is the hierarchy of journals in your field?
How significant are the findings or argument? The more significant, the higher you can aim.
Is your paper within the scope of the journal? Most journals will have a section called 'instructions for authors', 'guidelines for authors', 'information for authors' or similar — this will describe the content this journal is willing to publish.
What are the Open Access policies of the journal? You can use the Sherpa Romeo website to find this out.
Is your paper related to others in the journal?
Does the paper publish special issues?
Is the journal flourishing? Or is it always late or under-budget?
Sadly, there are some disreputable and unscrupulous publishers out there. Publishing with such outfits is not a good idea. The website Think, Check, Submit offers some guidance on things to watch out for when determining if a publisher is predatory.
Claire Sewell, Research Support Librarian (Physical Sciences) has also created a webinar on how to spot a predatory publisher.
You should not use citation metrics as the sole factor in choosing where to publish. There is no reliable way to accurately determine a journal's impact, and different platforms will give different impact factors for the same journal. However, should you wish to gain an impression of a journal's citation metrics, the following tools may help:
It is worth noting that Scopus only counts citations in journals which are indexed by Scopus, and Clarivate Analytics only counts citations in journals which it indexes.