ABM campaigns use the same channels as a traditional funnel approach, but with an enhanced level of either automated or manual personalisation and a lot more strategic thinking.
Retargeting, PPC /display adverts and programmatic approaches are key...but you need to work via a platform that allows you to direct these adverts at your target ABM list.
It's similar with events and conferences – you should only attend a conference or trade show if a large enough proportion of your target accounts are likely to attend. This could mean choosing to forgo an expensive stand in favour of organising a VIP lunch or dinner in proximity to the event and only inviting individuals who form part of your ABM campaign. Your Sales team can still network at these shows, of course. A ticket is considerably cheaper than a stand.
Direct mail is undergoing something of a resurgence at the moment and a well thought out, informative and memorable direct mail campaign to accompany your online efforts can only enhance your ABM campaign.