As the previous commenters said, start now and do not postpone this for any excuse. There are some agencies online that help you improve your resume. A colleague used it and has mixed feelings on the outcome but he said that it helped him get on with it (cost was around 100$). He also said that the best of that service was that they benchmarked his CV on automatic CVs parsers and did changes so that it passes the filters.
Do not forget your LinkedIN profile. If both resume and LinkedIN are outdated start from the latter.
Get some practice on interviewing as well. Friends and colleagues are your best bet for this. Once you feel more confident, apply to a couple of jobs that you don't care much about so you get some practice speaking about yourself and your achievements and the overall hiring process.
Found this post by @YtcWFjC-vkp to be some good advice for those who got cut.