When what you have presented leads up to, or supports, or makes a case for what you are about to say:
Therefore, 
Thus, 
Hence, 
Consequently,
We can see from the previous that, 
Because of the previous [sentence, paragraph, line of reasoning, three points,....] we can see that [or, it is rational to believe that, or it is reasonable to hold that]... 
In light of this we can see that

When you have given your conclusion first and want to then give your evidence, support, justification for it:
The evidence for ... is
The reason(s) for ... is (are)
One can see this because
This can be seen because
This is supported by

To do these sorts of things in one sentence, you can use words such as:
Since [x is true], [y is true]
Since [x], y ...
Because (of) x, y ...
Given that x, y ...
Factoring in that x, y...
Taking into account x, we can see that y...
As a consequence of x, y....
It follows from x, y
We can see from x, y

When you are going to "contradict" what has been said before [or contradict what you are about to say]:
However,
But
;
Nevertheless
In spite of this [or, in spite of the fact that ...,]
Despite [the fact that ..., ]
Unfortunately that does not....
Paradoxically
Contradicting that is
While it may seem that....
On the other hand
The apparent implication is that ... , but
While it may be that..., 
The previous does not imply/demonstrate/show
We cannot reasonably deduce/infer/assume from this that...
Although x, y ....
While it is the case that..., still....
While it is the case that..., it is not the case that (or it is not true that, or it is not to be inferred that, or it does not imply that....)

To link together similar things (whether ideas or reasons):
You can just number them
The following n things: [and then number them, or not number them -- whichever seems more appropriate]
Similarly
In the same vein
Along with
Accompanying that
Also
And
;
Additionally
In addition
Then too
Besides
Moreover
Further
Furthermore

To say that something is true in "both directions"
Conversely
The converse⁽¹⁾ is also true
And vice versa

To say it is true in only one direction:
The converse is not true.
This only goes in one direction.
This is only true in this direction.

To explain something further:
For example
Examples of this are
To clarify, ...
To say this in another way,
In line with that, ...

To change topics:
Moving on to a different point
Considering something totally different now, 
Let me digress for a moment...
Returning from the digression....
Returning to the above point about ....
Related to ....

Using physical structure, rather than words -- often good for introducing remarks related to a particular point or place, but remarks which are distracting or somehow peripheral even if they are important:
Footnotes
Endnotes
Parenthesis or brackets or braces
Indentations (from one or both sides)
Tables
Sidebars
Hyperlinks (internal or external)
Font changes (size, color, bold, italics, or a combination of these)
Headings and sub-headings
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1. In normal language, "converse" is not always used in the sense it is in doing mathematical or philosophical "logic" as a formal study. We may say, for example, in normal language that the groom not only gave the bride a ring at the wedding, but conversely she gave him one also. Or we may say that Sue loves Bill, and conversely, he loves her.  The Hatfields do not trust the McCoys, and conversely.  In this sense, converses are reciprocating actions or characteristics.

In formal logic, converses have a specific meaning, along with some implications of that meaning. The formal or logical converse applies to statements such as "if a (is true), then b (is true)", where the converse is "if b (is true), then a (is true)". We can leave out the parenthetical part and just say, the more usual, the converse of "if a, then b" is "if b, then a". Moreover, since "if a, then b" is generally the same as "all cases of a are also cases of b", or, for short, "all a's are b's", the converse is "all b's are a's." And, another way of saying "if a, then b" is "a is sufficient for b," since if whenever a is true we know b is true, it is sufficient to know a is true in order to know b is also true.

Now when "a is sufficient for b's being true" it follows that "b is necessary for a's being true." Consider: "knowing someone was murdered is sufficient for knowing they are dead." This implies that "knowing someone is dead is necessary for knowing they were murdered."

Finally in this regard, "if a then b" also implies that "a is true only if b is true". Consider: since "if you were murdered, you are dead." Then that implies you were murdered only if you are dead. 

[The "if/only if" relationship and the "necessary/sufficient" relationships are not always intuitive or easy to see how to word. I usually have to go through the "murdered implies dead" analogy to keep it straight. The converse of "if you were murdered, you are dead" is not necessarily true, because you can be dead without having been murdered. An example of converse statements which are both true can be found in testing to see whether a baking cake is finished baking or not. You can test the doneness of a cake by sticking a toothpick in its center and pulling it out. If the toothpick comes out clean, the cake is done; if the cake is done, the toothpick will come out clean.  There are other relationships (contradictions, contrapositives, contraries, etc.) in logic; there is no need to go into them here.]

or
a only if b

or
all a's are b's

or
a is sufficient for b 

or
b only if a

or
all b's are a's

or
a is necessary for b
(or b is sufficient for a)

or
all a's are b's and all b's are a's

or
a is necessary and sufficient for b
(or b is necessary and sufficient for a)