Garry Jones says doing so will avoid "ineffective, knee-jerk reactions", adding that the public expect "a level of security commensurate with risk".
"Event organisers need to have a way of systematically reviewing the threat to their event and their vulnerability to the ever-changing attack profile," said Garry, a member of the Institution of Occupational Safety and Health's (IOSH) Sports Grounds and Events Group and co-founder of event security and crowd management consultancy Storm 4 Events.
"You have got to know and understand a potential attacker's mindset, attack type and event vulnerability from specific attack types before you can implement mitigation measures.
"Once you know how vulnerable your event is, the hardest question is what you should do about it. You need to know the options available and their capability. Mitigation is scalable, based upon threat and vulnerability."
Garry said it is crucial that those assessing risks and mitigation tactics are fully competent to do so. He said possible tactics range from "explosives detection dogs and search providers to behavioural detection".
On 22 May 2017, a bomb was detonated as people were leaving a concert at Manchester Arena. Twenty-two people died, including some children, while hundreds more were injured.
With authorities regularly warning that other attacks are likely and the UK's threat level currently at 'severe', more than 100 event organisers, sports ground operators and other business leaders attended a counter terrorism event held by IOSH at Manchester United FC's Old Trafford stadium on Tuesday 15 May.
Sue Storey, also a committee member of the IOSH Sports Grounds and Events Group and Director of Sport and International Development at the Sports Grounds Safety Authority (SGSA), said organisations "cannot be complacent around safety".
She said one form of mitigation organisations can take is demonstrating how seriously they take security, including posting relevant information on websites.
"If people look at your website and there are images of heavy security presence and CCTV cameras, this shows you are really hot on security," she said.
"Put the messages out there that people should arrive early and expect to be searched. This also shows the customers how seriously you take it."
Andrew Donaldson, a former UK Government Counter Terrorism Official, said it is important to recognise the constantly changing ways that terrorist activity is planned and carried out.
He said that attacks now take much less time to plan and carry out and that there is an array of different attack types possible, including the use of vehicles and radiological devices.
Organisations, he said, need to widen their mitigation measures to factor these in.
