First, you are talking about at least three dimensions:
- Contribution: In most but not all disciplines, first authorship often denotes greater contribution. Other indicators include being one of a smaller list of authors (e.g., being second author on a two author-paper compared to a ten author paper).
- Quality: The quality of your papers; this can refer to the actual quality of the paper as judged by experts who read it; equally, some will judge quality based on the reputation of the journal or other indicators such as citations to the article.
- Quantity: Number of papers.
You could also contrast total career output versus recent average annual output. Total career output speaks somewhat to your overall reputation, whereas average annual output speaks to how productive you are both in general, and in recent years. This distinction is more important when people are comparing output of researchers with varying career lengths. In the case of comparing graduating PhD students for post doc positions, this distinction is often less relevant.
More generally, there is substantial variation in how contribution, quality, and quantity are weighted to evaluate you as a researcher.
In general, people evaluating you want to see lots (high quantity) of high (or at least good) quality papers with a decent number of first authorships, and see that this productivity has been sustained in recent years.
Of course, the amount of your time required to generate a given output is broadly related to the value assigned to it by people evaluating your research. On average, higher quality papers where you are the lead author take more time to write than lower quality papers where you are playing a support role.
Given the huge variation across disciplines, countries, universities, academics, it's difficult to give general advice. But here are some general comments.
- Try to get a few good first-author papers. But also get involved with other people's papers. This shows that you can collaborate. And in the cases where "number of papers" matters, playing a support role can speed up the process.
- Ask around to get a sense of the relative importance of journal rankings / impact factors / journal reputation in your area.