A few things:
1. Flaw training. The BJCP study guide has instructions for self-doctoring. Siebel and Aroxa sell kits for doctoring as well (I've worked with both and both are good, but there are others out there too). They are more expensive and need lead time (you may not have enough), but will cover attributes that are harder to self doctor.
2. Get used to writing your sheets fast. In the exam you have 15 mins per sheet. In the real world it's more like 10 mins. So practice writing a *master* level sheet in 10 mins.
3. Don't bother with guessing a style. The beer you're guessing may represent nothing and you won't be tested like that. You'll be told the style. Evaluate against what you're told, that's it. Many commercial examples don't represent styles any many styles have hard to find accurate examples. Practice evaluation is good. Blind is also good. But evaluate it against the guidelines. Seek out the listed examples to calibrate (while also realizing even then few are perfect examples).
4. Focus on writing good sheets.
-Discuss *everything*. If the sheet mentions it, say. "No other aromatics". "No creaminess". The only catch, the sheet doesn't mention hop flavor AND bitterness, but you need to mention BOTH on all sheets "no hop flavor, moderate bitterness". In sets I grade that can sometimes be a deciding factor for a borderline Certified/National tasting exam. Bottom style/flaw/intangible range boxes checked every time. Any descriptor boxes checked, and not only if flaws. Officially lower than "low" perception doesn't need it, but if you list it, check it.
-have your wife work with you. Back to back. Describe the beer verbally. Have her write a scoresheet without tasting or seeing the beer, only based on your description. Better if done with another prospective judge, who can ask questions. When you're done, trade places and do it with a different beer. You want to be able to fully and accurately experience the beer through that written description. If not, you're not descriptive enough. It'll help you learn the level of description needed. And it's a technique used to train exam proctors that you'll be evaluated against when taking the exam.
-feedback is tough and where almost everyone struggles. I want to see your style and technical knowledge shine. Want you to connect dots. But don't make assumptions. Justify why you scored what you did, and give the brewer instructions to make it better. The challenge is to give feedback that is both actionable (a specific correction), but doesn't assume anything, and is both stylistically and technically accurate. If there are stylistic or technical faults, provide feedback for *every* *single* *one*.
On a master level sheet, writing small, you should be FILLING appearance and mouthfeel, and often into the margins on aroma, flavor and overall impression.