nuk gabe is partially right. Arimidex used to be the panacea to preventing conversion of test to estrogen during cycle. however what was found is that arimidex:
1. caps at 50% estrogen inhibition no matter the dosage
2. royally fucks up your lipid profiles
the new panacea to AI's is aromasin. 6.125mg-12.5mg ED should take care of most of your guys cycles. Anything over 1200mg of test may require more however.
EDIT: Do not take a SERM while on cycle; reserve them for PCT and for PCT clomid suffices at 50mg ED for 4 weeks.
Just make sure while on cycle to run HCG, and an AI, and then for PCT run the AI through as well with the SERM.