tips for editing old writing:
1) The most obvious method - read through it, editing anything that stands out to you as you go along.
2) Read it aloud - Haven't really done this myself, but it can help a lot if you have problems with grammar or English is your second language. Anything that sounds weird, or you really have to think about how you should say it, you should probably edit.
Things to pay particular attention to while editing: tenses. It's really, really easy to accidentally slip into the wrong tense while writing.
Perspective. Make sure you don't slip between 1st and 3rd person and narration without making it crystal-clear which is which. Which, I suppose, brings us to the other part of your question.
Transitions. There are lots of different places transitions can be used: character transitions, scene transitions, time transitions, chapter transitions, and so on and so forth.
Since you mentioned having difficulty with ending chapters, I'll start with that. Now, you're probably familiar with cliffs, or cliff-hangers, where you end the chapter on a point of high suspense - a sentence half spoken, at the climax of a battle, you likely know the sort of thing I'm talking about. As with so many things, less is more. The less often you do this, the more impact it'll have when you do. Inversely, the more you do it, the less impact it'll have and the more it'll annoy your readers. On the other hand, if the situation calls for it, like if you're nearing the final battle, it'll only build up the suspense even more, and it's definitely something you should consider doing.
Sometimes you might find that you have to split something into two chapters, but you don't want it to be a cliffhanger for the above or other reasons. In that case, you'll want to end the chapter on a low to mid suspense sort of feel. So rather than ending the chapter as the dark lord raises his dark blade to chop down at the hero who has stumbled, you have the two engage in a clash of blows and/or magic, with neither really coming out with a massive advantage, and end the chapter in the slight pause after they disengage. Of course, this isn't exactly specific to fighting. You want to end on a point that doesn't feel like it's near the end nor the beginning of whatever activity is in question, at a point that feels natural. Like the end of a part of that activity. For combat, a clash, for crafting, a component, for learning a class, and so on.
But most of the time, you'll just want to finish at the end of something, although it may sound pretty obvious. The end of a fight, the end of a conversation, and so on.
But maybe you're less questioning the when, and more questioning the how? Well, first things first, don't start the last sentence of your chapter with 'and so', unless you're using it ironically or sarcastically. Other than that, it's pretty free-form. You could even end a chapter with "Huh." if it was contextually viable. I suppose it goes back to what I said before, end at the end. Not just literally, but metaphorically as well. It has to feel like the end of whatever it is. For instance, if you're finishing on a conversation, and you don't want to finish at the literal end of the conversation but, for instance, after they have finished discussing something critical to the story, you might want to write a short sentence mentioning that they kept chatting for a while, or something similar.
As for other types of transitions, you need to clearly define to the reader that there is a transition. Imagine that your readers are incredibly stupid for a moment, and do what you must to make them notice the change. Obviously, most of them won't be incredibly stupid. But every now and then you get one who is. I once had a guy comment that they were confused about a character transition. My general template for doing character transitions is to have a horizontal line, then have the name of character whose POV i'm switching to right below it, centered and very clear. Not much more I can do after that besides just making the text bigger.
But anyway. Character transitions are, in my opinion, the most important transitions to make sure the reader gets. Time transition? Can be important, but generally very few people will be keeping track of time, and those sort of people will likely be paying more attention anyway. Scene? Also important, but it can be very simply explained, and will likely be referenced every now and again thereon. But character transitions are difficult. Unless the character is constantly like, 'I am joe and joe is my name', people will have to rely on their thoughts and interactions with others to try and determine which character they are following. This can often be made clearer with dividers of some type between different character perspectives and by initially stating the name of the character. Another way I've seen this done apart from the way I mentioned in the previous paragraph is by separating different perspectives into different chapters. Not to say that every chapter was a different perspective, but that if a perspective changed, it would be at the start of a chapter, and the name, again, would be immediately evident.
You're concerned about your character being a go-with-the-flow kinda guy? Not much of a problem. I mean, quite a few people are. What you can do is use it for some character development. Force the character into a leadership role, or make him face personal dilemmas that nobody can help him with. Then you have the unspoken question of whether your character will step up to the role, and grow as a result, or crumble under the pressure.
Worried about your plot being too obvious? Yeah, I think quite a lot of us are. Personally, I constantly worry that I'm giving way too many clues and foreshadowing as to the end events of the novel. I think I've said this somewhere else, but I think a general guideline to follow is that the vagueness of the foreshadow should be proportional to how far away in the story it will be relevant. Something happening in the far future should barely be hinted at (or not at all), while something happening that chapter should be almost (if not actually) stated.
