It always helps if you can get a good recommendation letter because it benefits the application process and you stand a good chance of making it. Prefer to get this from someone who knows you sufficiently well and always ask him in person. Take these letters from your teachers/professors if you want a letter for graduate schools or college. If the letter is meant for a business, job or professional school it’s advisable to get it from your current company. If you haven’t been in touch with the current company for long then you may ask your previous company.
Make the request for this letter beforehand rather wasting time running after it in the last minute. If the letter is for academic purpose request your professors/teachers one month in advance. If it is for job in a new company, ask from your previous employer when you leave the job.
While making the letter, supply the writer with relevant information for instance the resume. Be honest when you furnish this information.