Hello,
So I made this guide for me so I can just copy-paste the commands but later I thought that I will decorate it a little and make it public. I hope you will like my guide and find it useful.

Just select the play with bots mode and copy paste the following console commands for a perfect Nade practice server.

Just copy paste the following in your console:
The console in csgo only allows a limited number of characters at a time. So for your convenience I have made 2 parts of commands so you can copy 1 at a time.

Part 1:
sv_cheats 1;
bot_kick;
mp_limitteams 0;
mp_autoteambalance 0;
mp_maxmoney 60000;
mp_startmoney 60000;
mp_buytime 9999;
mp_buy_anywhere 1;
mp_freezetime 0;
mp_roundtime 60;
mp_roundtime_defuse 60;
mp_respawn_on_death_ct 1;
mp_respawn_on_death_t 1;
sv_infinite_ammo 2;

Part 2:
sv_grenade_trajectory 1;
sv_grenade_trajectory_time 15;
sv_showimpacts 1;
sv_showimpacts_time 10;
ammo_grenade_limit_total 5;
god;
bind k "noclip";
bind o "sv_rethrow_last_grenade";
mp_warmup_end;
mp_restartgame 1;

Copy the following commands only if you want to know where the grenades will land before you throw them.
cl_grenadepreview 1;
bind j "cl_sim_grenade_trajectory";

This section contains the key bindings we used in the console commands above.
Note: You can change the binds by simply replacing the bind key in the command. For example, if you want to bind noclip key to M and not K then you can replace the 'k' in the console command with 'm' i.e. bind m "noclip";

K: This key is binded to noclip. Pressing K will allow you to traverse through the map like a super saiyan. The uncool part is there will be no super saiyan aura around you. Press the same key to reverse the effect.

O: So you just discovered a game breaking line-up for a pop flash and you just want to know to what extent your enemy gets flashed or at what positions? Fear Not, Just do your line-up then go to the location you want your enemy to be and press this key. This will replay your last thrown nade. Also, it is very fun to throw a molotov and then spam this key, just saying.

J: This bind will only work if you copied the second part of the console commands. So what this key does is, it saves the trajectory of the grenade you are throwing. To do that, hold your left key or right or both and press the key you will see the trajectory of the nade has been saved. You can save multiple trajectories at the cost of your fps but don't worry those will disappear after 15 seconds. You can use this command to remember your previous lineup and try few changes in that to see how it turns out.

This section will explain every command individually so you can customise the settings further more:
sv_cheats 1: This enables Cheats.

bot_kick: Kicks all the bots from server.

mp_limitteams 0: This command sets the maximum amount of difference in number of players
possible in two teams. Setting this to 0 disables the check.

mp_autoteambalance 0: This command can be used to enable or disable the auto team balance feature.

mp_maxmoney 60000: This increases the maximum amount of money a player can accumulate to 60000$.

mp_startmoney 60000: This changes the starting money of the game to 60000$ (Default is 800$).

mp_buytime 9999: This command sets the amount of buy time available after start of round (in seconds).

mp_buy_anywhere 1: This allows the players to buy anywhere on the map.

mp_freezetime 0: This command sets how long players are frozen for at the start of each the round.

mp_roundtime 60;: Sets the round time to 60 minutes.

mp_roundtime_defuse 60: Sets the round time to 60 minutes in defusal game modes.

mp_respawn_on_death_ct 1: This command will set whether or not counter-terrorists will respawn after dying.

mp_respawn_on_death_t 1: This command will set whether or not terrorists will respawn after dying.

sv_infinite_ammo 2: This will give you infinite ammo. (With reload. If you don't want to reload change the value to 1).

sv_grenade_trajectory 1: This command shows the trajectory of grenades.

sv_grenade_trajectory_time 15: The time before the grenade trajectory disappears (in seconds).

sv_showimpacts 1: Used to show bullet impacts (Red squares are client side impacts and Blue squares are server side impacts).

sv_showimpacts_time 10: This command sets the amount of time, in seconds, that bullet impact squares show for before they disappear.

ammo_grenade_limit_total 5: Allows the player to get hold of 5 grenades instead of 4.

mp_warmup_end: Ends the warmup.

mp_restartgame 1: Restarts the Game.

god: This enables god mode (No damage).

noclip: No clip allows the player to fly through the wall.

sv_rethrow_last_grenade: Replays your last thrown grenade.

cl_grenadepreview 1: Allows you to see the trajectory of the grenade before throwing by holding left or right mouse button.

cl_sim_grenade_trajectory: Saves the current trajectory of the grenade (You need to hold left or right mouse button before using this command.)

bind key "command": This allows you to bind a key to the command so you don't have to type it repeatedly in the console.