Since you give no specifics, my advice can only be extremely generic. I will assume that you have already made a preliminary choice of a journal (which these days is far from easy, given the large number of predatory and otherwise "fake" publishers) and have made sure that you can fulfill their publication requirements (fees, copyright agreements etc.). I will also assume that you own the intellectual property of the MS (which may not be true if you wrote the MS while on the payroll of a company or certain other types of employers), or in the case of a multi-author MS that you are acting in agreement with your co-authors. If any of the above does not apply, don't submit anything for publication until all these points are cleared.
1. Read the journal description, especially the type of topics that the journal states as acceptable. Based on this, decide whether your MS fits the journal scope.
2. Read one or more recent issues of the journal to make sure your intended paper fits the journal scope and style.
3. Read - several times - the instructions for the preparation of manuscripts and illustrations. Re-check these rules while preparing the MS, any time you are in doubt. If you still have unanswered questions, ask the journal editor(s). Also make sure your MS complies with styles etc. of recently published papers in the same journal.
4. Submit the MS in the format, number of copies etc. required by the journal.
5. At the time of submission, it generally helps to suggest the names of two-three professionally competent reviewers, preferably people who already know you and/or your work and whom you can be reasonably certain to accept to review your MS. Don't suggest as reviewers very famous and extremely busy scientists totally unaware of your existance, because this will destroy your credibility. The editor is of course not obliged to use the reviewers that you suggested, but your suggestions may help in restricted fields in which the editor may have no specific personal contacts.