These terms are ambiguous and have fluid meaning. But in general, anything on the Republican party platform, or supported by a substantial portion of Republicans or self-identified conservatives, is something I would consider part of mainstream conservatism. Quick examples include:
* That affirmative action should be illegal or more heavily restricted.
* That unlawful residents should be removed from the country, even if previous administrations chose not to enforce immigration law.
* That welfare programs should be cut back.
* That taxes should be reduced, even if they're reduced in such a way that the wealthy receive a greater tax cut than the non-wealthy.
* That restrictions on firearms purchases and ownership should be kept permissive, and that restrictive local laws (e.g. California's) are unlawful.
* That the US should be more restrictive in allowing foreigners to work in the country (e.g. raising the minimum salary for H1B workers)
* That inequalities in education, employment, and achievement should not be presumed to be indications of bias.
These are just quick examples. Personally, I advise anyone to conceal their political leanings if they agree with any of these statements in my current workplace if they wish to preserve their career prospects, and I think that's a shame. All of these are things that half to 30% of the voting population believes in, and are on the core platform of one of the two major US parties. Any workplace that claims to tolerate conservative views should tolerate these statements.
"Conservative", "liberal", "centrist", etc. are by no means monolithic attributes. I think these labels are better described as broad generalizations of individual positions on issues. For example, I agree with 70-80% of "liberal" positions (maybe closer to 60% if you include San Francisco local issues, but there's arguments to be made that's more "far-left" vs. "left" than liberal vs. conservative). I still consider myself a liberal. That said, I still do censor myself on any non-anonymous forums for the remaining 20-30%.