Instantiating widgets
The answer really depends on what you're building. For example, if you're building a grid of labels and entry widgets then a simple data structure and loop is all you need. For example:

fields = [
    {"id": "sys_desc", "label": "System description", "default_value": ""},
    {"id": "model", "label": "Model", "default_value": ""},
    ...
] 
self.labels = {} 
self.entries = {}     
for field in fields:
    label = tk.Label(self, field["label"], ...)
    entry = tk.Entry(self, ...)
    entry.insert("end", field["default_value"])

    self.label[field["id"]] = label
    self.entry[field["id"] = entry

self.label["sys_desc"].grid(...)
self.entry["sys_desc"].grid(...)
...


Another solution is to create a helper class or helper function so that your code looks something like this:

self.add_widget(self, "sys_desc", "System Description", "default value...", row=1)
self.add_widget(self, "model", "Model", "default model", row=2)
self.add_widget(self, "serial", "Serial Number", "default serial value", row=3)
...


Or with classes:

self.sys_desc = LabelEntry(self, "System Description", ...)
self.model = LabelEntry(self, "Model", ...)
self.serial = LabelEntry(self, ...)
...


There is no single answer for all layouts. Complex layouts require complex code, simple layouts can be built with simple code. The bottom line is to look for patterns, and make helpers to help reduce repetitive code.