Remove margin in android toolbar icon

You can adjust the margins by modifying the theme and style, like this：

<style name="cusToolbarNavigationButtonStyle" parent="@style/Widget.AppCompat.Toolbar.Button.Navigation">
    <!--default is 56dp-->
    <item name="android:minWidth">0dp</item>  
    <item name="android:paddingLeft">16dp</item>
    <item name="android:paddingRight">16dp</item>
</style>

<style name="cusToolbarStyle" parent="@style/Widget.AppCompat.Toolbar">
    <!--default 4dp-->
    <item name="titleMargin">0dp</item> 
    <!--default @dimen/abc_action_bar_content_inset_with_nav-->
    <item name="contentInsetStartWithNavigation">0dp</item> 
</style>
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">

    <item name="toolbarNavigationButtonStyle">@style/cusToolbarNavigationButtonStyle</item>
    <item name="toolbarStyle">@style/cusToolbarStyle</item>

</style>

if you are using this

   <android.widget.Toolbar>
    android:contentInsetStart="0dp"
    android:contentInsetLeft="0dp"
</android.widget.Toolbar>

if using

    <androidx.appcompat.widget.Toolbar>

    app:contentInsetStart="0dp"
    app:contentInsetLeft="0dp"
</androidx.appcompat.widget.Toolbar>

You can easily remove Margin | padding between title and back icon with:

app:contentInsetStartWithNavigation="0dp"

Margin | padding In left/right side of toolbar with:

app:contentInsetStart="0dp"

Also if you need more customization do with following:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="@color/color_primary"
    app:contentInsetEnd="0dp"
    app:contentInsetLeft="0dp"
    app:contentInsetRight="0dp"
    app:contentInsetStart="0dp"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center_vertical">

        <ImageView
            android:id="@+id/icon_toolbar_left"
            style="@style/IconFont.Large"
            android:layout_width="48dp"
            android:layout_height="match_parent"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:background="?attr/selectableItemBackground" />



        <TextView
            android:id="@+id/text_toolbar_title"
            style="@style/Textview.White.MediumSmall"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_toLeftOf="@+id/icon_toolbar_right"
            android:layout_toRightOf="@+id/icon_toolbar_left"
            android:gravity="center"
            android:text="@string/nav_category"/>


        <ImageView
            android:id="@+id/icon_toolbar_right"
            style="@style/IconFont.Large"
            android:layout_width="48dp"
            android:layout_height="match_parent"
            android:layout_alignParentEnd="true"
            android:layout_alignParentRight="true"
            android:background="?attr/selectableItemBackground"/>

    </RelativeLayout>

</android.support.v7.widget.Toolbar>