Hi, Wow! Big subject...
Editing or Proofreading - Most use the terms interchangeably, but they focus on different aspects of writing and employ different techniques.
Editing - this is corrections to the structure, your style, the flow of the narrative, timelines, if you like who, what, when, where, why, and how, all of these would be strictly speaking part of the editing process. There is no easy way to address these, but read through identify them and correct with cuts and rewrites.
Proofreading - is more a focusing on surface errors checking out each sentence for its Grammar, Punctuation, Spelling and correct word usage. This includes typo errors; extra spaces, missing periods, left off quotes in speaking parts, no Upper Case letters at the start of a new sentence; etc. etc.
Grammar – In general I try to keep sentences reasonably short, around fifteen words or less is a good guideline. Write sentences so they flow well together. Long sentences can get unwieldy. If cutting into shorter segments does not blend smoothly, then try to rephrase or add connective phrases. Refrain from using the same word and phrases too often as it makes your work sound repetitive. A Thesaurus can be a helpful tool when struggling to find the right word.
Punctuation - [ . ? ! “ ” ‘ ’ , ; ] missing; period, exclamation or question marks, speech quotes, or comma crazy with unnecessary punctuation, marking possessives apostrophes (Mother’s) and leaving them off if a plural (Mothers) and not forgetting brackets, hyphens, dashes and Capital letters signalling special use of words.
Spelling - software spellcheckers can be limited in their capabilities, they often do not recognise proper names and technical terms. In addition, they cannot detect where the user has entered a wrong word in place of the proper one. Such as common confusables, like ‘there’ when you meant ‘their’ or possibly even ‘they’re’ and words like it’s/its and to/too.
Depending on your writing skill, by the first draft of your manuscript, a good deal of the most common Grammar, Punctuation, Spelling and typo errors, will hopefully have been spotted and corrected. In Editing and Proofreading, the trick is not to look for everything in one go, just read through several times and focus on a different feature at each pass. Finally, I recommend this technique to check your manuscript. Read aloud (or by using a text-to-speech generator) each page top to bottom, but in reverse order (namely, last page to first).
Note: Caution! Gain plenty of experience in writing before attempting clever wordplay unless you are sure that it will work.
This is my general guide for Editing/Proofreading
01 First Draft - Your manuscript is complete or so you think. This is your first read through end to end. You can use the proofing capabilities of your word processor to check for basic Grammar, Punctuation, and Spelling errors. Does it meet with your expected criteria and tick all the boxes in following your Storyline?
02 Timelines - As you read through, check the chronology of events are sequenced correctly within the context of the storyline. In addition, check spelling of Character names, place names; etc. are consistent.
03 Word Usage - This time check for word usage and common confusables. For example, should you have used affect, or effect, always not all ways, berth or birth, forward not foreword, holey or holy?
04 Text-to-Speech - Now it is about time your manuscript was read back to you. One way is to use a text-to-speech generator. This can help in spotting incorrect sentence construction, missed words, punctuation errors, and word tenses, their endings or miss spelling.
05 Second Draft - Check your errors are corrected and take the opportunity to cut ruthlessly any irrelevant text.
06 Grammar - This is when you try to put right those sentence constructions that don’t quite hang together. The Grammar & Style checker on your word processor may help in highlighting some of these.
07 Punctuation - In this read through, check for Punctuation marks missing or inserted unnecessarily.
08 Spelling - A final check to identify any Spelling errors, and importantly that individual word usage is correct for what you are trying to express. [FONT=&]. [/FONT][FONT=&](such as - Internment/Interment; Moral/Morale)[/FONT]
09 Critique - At some point, you need an independent review of how your Storyline hangs together, plus any other Grammar, Punctuation, miss-Spelling, proper word usage; etc., that you might have overlooked. For minimal cost, it is time to get family members and/or friends to read your manuscript.
10 Final Draft - Having reviewed Critiques and corrected those areas you agree are necessary, you decide if the manuscript finally meets the criteria for publication.