the place of adverbs is usually after the verb, they go after the main verb,eg. she speaks slowly. but adverbs are frequency are different,like l usually have lunch at 1. though in the case of a to be verb it is different ,e.g:lt is usually rainy here in winter.

Both are fine. Normally you put the adverb before the verb, but it is very possible to move it around. Within reason, of course (eg. don't put it in front of a noun, adjectives go there). It's a really subtle difference: "I grimly tried..." focuses on the grim feeling ahead of the action. "I tried grimly..." focuses on the action. Grimly is extra information: "I tried, grimly, to suppress the feeling." I would prefer this second option because the early adverb in the first sentence distracts the reader from the action.

I think it is" I tried grimly...