I would recommend giving a cold mock and understanding where you stand currently in term of scoring (make sure you are familiar with the exam pattern and timing and number of questions etc.)
Based on that I would say you can gauge if you need to subscribe to any courses or not (courses and professional help can boost prep though).
I would say that if you are scoring anywhere above ~450 then you can (not SHOULD) do it independently without a course - gauge which section is your weakest and start working on that. The official guide and manhattan are good resources to start with basics. Get familiar with topics and PRACTICE as you learn (GMAT club
forum quiz is one of the best places to practice).
Once you're confident on the ability - make a mock routine (get a mock subscription ) and follow and keep working on 3 things:
1. Gauging your best section (Quant, DI or verbal) and setting your preferred order of sections in tests.
2. Anxiety management during less time.
3. Analyzing your scores and mistakes IN DEPTH - painful but the most beneficial for improving scores.
Also do not take mock scores to heart. Only the one you get in GMAT attempt matters

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All the best for your preparation!!