OG question types are very similar but you'll notice that people who do well take a lot of CATs. There is something different from eliminating answers off a paper and computer. GMATPrep (two tests) will forcast your score to within 20 points so you should take that before you take another GMAT. With 5 GMAT scores, AdCom is going to be wondering what's going on so your next (and LAST) should be above your 550 mark.
I'm also going to guess you haven't bought
MGMAT. Get it, people who use it get good scores because it stresses the basics.
Basic tricks...
1. Reading Comp - Eliminate all extreme answers
2. Sentence Correction - look for 3/2 split
3. Critical Reasoning - eliminate all out of scope answers
4. Data Sufficiency - AD or BCE (if the answer is A the only other is D, if B then only CE remain)
5. Data Sufficiency - if you don't know A, start with B
6. Data Sufficiency - if you say the answer is "no, x doens't = 5" the pick is correct (people will sometimes eliminiate it by accident)
7. Sentence Correction - go down checklist of (Subject-Verb, Modifiers, Comparisions, Parallel, Verb Tense, Idioms, etc.)