The technique I use is I reach my hand behind my back and grab hold of the object I hope to summon. Once I feel it I can bring it Infront of myself and I can start using it. This works because it is much easier to visualize tactile sensations than visual ones. This also works for summoning people. Just imagine feeling the person's hand behind you. For summoning people I recommend having a quick back and forth of dialogue before bringing them forward to make sure they are the right person.